Medications · Hormone optimization

Progesterone

Bioidentical progesterone for HRT and gynecologic care.

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Progesterone molecular structure (Bioidentical progesterone)

Why this needs to be personal

Why Personalized Progesterone

Prometrium was approved at 100 mg and 200 mg oral capsules. Crinone was approved at 4% and 8% vaginal gel. Those strengths and routes were chosen because they cleared the endpoints the FDA wanted to see, endometrial protection in combined HRT and luteal support in IVF. The trials did not pick a dose for your baseline progesterone level, your sleep response, your sensitivity to peanut-oil excipient, your tolerance for the next-morning grogginess that oral micronized progesterone produces in some women, or where you actually sit in the perimenopausal transition. They picked one dose for a population.

Compounding is what closes that gap. The molecule is the same bioidentical progesterone the FDA reviewed in Prometrium. RonanRx can prepare it at a custom oral strength between the standard 100 mg and 200 mg when a prescriber is titrating sleep or mood response, as a peanut-oil-free troche or capsule for patients with peanut allergy or excipient sensitivity, or as a vaginal suppository at a strength Crinone and Endometrin do not offer. For continuous combined HRT regimens that pair a specific estradiol dose with a non-standard progesterone strength, the compounded preparation is the only way to land both numbers on the same prescription. We are explicit about one limit, transdermal cream does not reach serum levels high enough to protect the uterine lining from estrogen, so cream is not the progestogen arm of a combined HRT regimen.

This is what pharmacy looked like before mass manufacturing arrived. A prescriber wrote the order for a named patient, and a pharmacist prepared it to match. Compounded progesterone is that older arrangement, kept honest by modern oversight.

In brief

Progesterone Explained

Progesterone is the body's main natural progestogen, the hormone the ovary's corpus luteum makes in the second half of the menstrual cycle, and the hormone the placenta makes in large amounts during pregnancy 20. Bioidentical micronized progesterone is the same molecule, prepared in a form the body can absorb.

Doctors prescribe progesterone primarily for two reasons: to protect the lining of the uterus in women who are taking estrogen for menopause symptoms, and to support pregnancy in assisted reproductive technology (IVF) or to prevent preterm birth in women with a short cervix 10111. There are FDA-approved products for each of these uses, Prometrium (oral capsule), Crinone (vaginal gel), and Endometrin (vaginal insert).

RonanRx can also compound bioidentical progesterone, a custom-strength oral capsule, a vaginal suppository at a strength the manufactured market does not offer, a troche for patients who cannot tolerate the peanut-oil excipient in Prometrium, or a cream for a specific patient-prescribed use. We are explicit about one limitation: progesterone creams do not reliably reach blood levels high enough to protect the uterine lining from estrogen, so compounded creams should not be used as the progestogen arm of a combined estrogen-plus-progestogen regimen unless a different route is also in place 12.

Progesterone is not a controlled substance, but it is a prescription medication that requires evaluation by a clinician, with dosing and route chosen for the specific clinical reason 24.

At a glance

Quick Facts About Progesterone

Category
Endogenous progestogen (C21 steroid hormone); the principal natural progestogen in humans
Active ingredient
Progesterone (bioidentical, micronized), chemically identical to the endogenous hormone (pregn-4-ene-3,20-dione)
FDA-approved branded products
Prometrium (oral micronized capsule, 1998), Crinone (vaginal gel, 1997), Endometrin (vaginal insert, 2007). 17-α-hydroxyprogesterone caproate (Makena) was withdrawn from the US market in 2023 after the PROLONG confirmatory trial failed to replicate the original Meis 2003 benefit.
Routes studied in humans
Oral micronized (Prometrium), vaginal gel (Crinone), vaginal insert (Endometrin), intramuscular (progesterone in oil), and compounded routes: vaginal suppository, troche, rectal suppository, topical/transdermal cream
Evidence posture
Multiple FDA-approved manufactured products; foundational randomized evidence from PEPI (endometrial protection), WHI (combined estrogen-progestin arm with MPA), and large vaginal-progesterone preterm-birth program (Fonseca, Hassan, Norman OPPTIMUM, EPPPIC IPD meta-analysis). E3N observational cohort distinguishes bioidentical progesterone from synthetic progestins on breast safety.
FDA-approval status
Prometrium, Crinone, and Endometrin are FDA-approved manufactured products. Compounded preparations are not FDA-approved but address established patient-specific needs (custom strengths between 100 / 200 mg, alternative routes, excipient sensitivities, troches).
Compounded under
503A, patient-specific prescription only. Not a controlled substance.
Compounded role
Custom strengths the manufactured market does not offer (between standard 100 mg / 200 mg oral; vaginal compounded suppositories at specified strengths; female-physiologic compounded creams for adjunct use), troches for patients who cannot tolerate the peanut-oil excipient in Prometrium, and combination preparations on a documented patient-specific prescription. Routine substitution of compounded oral progesterone for Prometrium without a documented clinical reason is not within the FDA's 503A framing.
Notable caution
Transdermal progesterone cream produces serum levels that are inadequate to reliably oppose estrogen-induced endometrial proliferation; it should not be used as the endometrial-protection arm of a combined hormone-therapy regimen. The NASEM 2020 report addresses this directly.

Prescription review

Patient-Specific Prescription Only

Progesterone on this page is a 503A compounded preparation. Every dose is made on a prescription, for a named patient, by a licensed pharmacist. It is not a stocked, mass-manufactured product.

  • Made to order, not off a shelf. No batch sits in a warehouse waiting for buyers. Your prescription is what triggers the prep.
  • Named-patient label. The bottle carries your name. The batch records carry your prescription.
  • Dose, strength, and route chosen for you. A prescriber who knows your chart decides what gets compounded, not a manufacturer who set the strength for a trial population.
  • Licensed pharmacist on the hook. A real person, with a license that can be pulled, signs off on every prep. State inspectors check the facility.
  • Compounded drugs are not FDA-approved. They should not be evaluated using branded-drug trial data. Availability varies by state and prescribed medication.
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Real medicine, not gray market

How This Differs from a Research-Use-Only Website

A research-use-only website ships a vial from a warehouse. There is no prescription, no pharmacist, no facility inspection, and no way to recall the product if something is wrong with it. If the vial is mislabeled, contaminated, or under-potent, there is nobody whose license is at stake.

A 503A compounding pharmacy is the other thing. Your doctor writes the prescription. A licensed pharmacist, whose name is on the label, prepares the medicine in a facility the state inspects. If something goes wrong, there is a person and a license on the hook, and a documented chain of custody on every lot. That accountability is what makes it safe.

What it is

What is Progesterone?

Progesterone (pregn-4-ene-3,20-dione) is the principal endogenous progestogen in humans, a C21 steroid synthesized from pregnenolone, which is itself derived from cholesterol 41. In a non-pregnant cycling woman, the dominant source is the corpus luteum during the luteal (second) half of the menstrual cycle, producing approximately 20, 25 mg per day at peak. In pregnancy the placenta becomes the dominant source after roughly the 7th, 9th week of gestation and produces several hundred milligrams per day by the third trimester. Small amounts derive from the adrenal cortex year-round.

Bioidentical progesterone, the same chemical entity as the endogenous hormone, has been used pharmaceutically since the 1930s and 1940s 41. Oral bioavailability of unmodified progesterone is very low because of extensive first-pass hepatic metabolism. The modern oral formulation became practical when micronization (reduction to small particle size, suspended in an oil vehicle) substantially improved absorption 13. Prometrium (oral micronized progesterone in peanut oil) received FDA approval in 1998; Crinone (vaginal gel) in 1997; Endometrin (vaginal insert) in 2007.

Progesterone is structurally and functionally distinct from synthetic progestins (medroxyprogesterone acetate, norethindrone, levonorgestrel, drospirenone, and others) used in oral contraceptives and the original WHI combined-HRT regimen. Synthetic progestins are designed for selectivity, potency, oral activity, or progesterone-receptor binding profile, they are not equivalent to the endogenous hormone in receptor selectivity, metabolite spectrum, or adverse-event profile 40 39 4142.

How it works

How Progesterone Works

Class
Bioidentical progesterone
First studied
1934 (isolation)
Common forms
Oral capsule, troche, cream, suppository
Compounding category
503A, patient-specific prescription

Progesterone acts at the nuclear progesterone receptor (PR), a ligand-activated transcription factor expressed in two principal isoforms, PR-A and PR-B, encoded by a single gene with two promoters. The two isoforms have distinct, sometimes opposing, transcriptional programs: PR-B is the principal transcriptional activator in mammary gland and several reproductive tissues, while PR-A is dominant in uterus and is required for normal reproductive function. Isoform-selective knockout mice established the in vivo separation of function 37 38.

Beyond classical genomic PR signaling, progesterone has rapid nongenomic effects through membrane-associated progesterone receptors (mPRα, mPRβ, PGRMC1) and is the precursor for the neurosteroid 5α-pregnan-3α-ol-20-one (allopregnanolone), a potent positive allosteric modulator of the GABA-A receptor 35 36. The GABA-A modulation by allopregnanolone is mechanistically distinct from synthetic progestins (which do not reliably generate allopregnanolone) and underlies progesterone's sedating, anxiolytic, and anticonvulsant properties. The FDA approval of intravenous allopregnanolone (brexanolone, Zulresso, 2019) for severe postpartum depression is the clinical proof of this mechanism 34.

Endometrial action is the best-characterized clinical effect of progesterone: in estrogen-primed endometrium, progesterone induces secretory transformation, opposes estrogen-driven mitogenic activity, and prevents the development of endometrial hyperplasia and carcinoma. The PEPI trial 1 established that micronized progesterone (200 mg cyclic 12 days/month) protects estrogen-primed endometrium at a rate equivalent to medroxyprogesterone acetate, with markedly less hyperplasia than estrogen alone. The vaginal route exploits a first uterine pass effect: vaginally administered progesterone concentrates in the uterus at concentrations several-fold higher than serum 15 16.

Research history

Progesterone Research History

Progesterone was isolated in 1934 by four research groups in rapid succession (Butenandt, Slotta, Hartmann, and others), with characterization of the molecule and total synthesis from cholesterol following over the next several years. Early clinical use was limited by the very poor oral bioavailability of unmodified progesterone, which drove the development of synthetic progestins in the 1940s and 1950s, pharmacologically active orally and patentable, but not structurally identical to the endogenous hormone.

The modern era of bioidentical oral progesterone began with Hargrove and Maxson's 1989 demonstration that micronization (reducing particle size and suspending in oil) substantially improved oral absorption 13. Subsequent pharmacokinetic and pharmacodynamic work by de Lignières and colleagues 14 characterized the oral micronized progesterone profile and its applicability to combined hormone therapy. Prometrium received FDA approval in 1998.

The vaginal route emerged in parallel. De Ziegler and Bulletti demonstrated the 'first uterine pass effect', preferential uterine concentration after vaginal administration 15, and Cicinelli confirmed the uterine-artery vs systemic gradient 16. Crinone vaginal gel (FDA 1997) and Endometrin vaginal insert (FDA 2007) followed, principally for luteal support in assisted reproduction.

The PEPI trial 1 established that oral micronized progesterone 200 mg cyclic protects estrogen-primed endometrium as effectively as MPA, the foundational endometrial-safety evidence for bioidentical progesterone in combined menopausal hormone therapy. PEPI's endometrial-histology analysis remains a touchstone in NAMS and Endocrine Society guidance 10 11.

The WHI combined-HRT arm 2 was stopped early in 2002 for an excess of cardiovascular events, breast cancer, and venous thromboembolism in the estrogen-plus-MPA arm. The estrogen-alone arm in hysterectomized women 3 showed a different signal, no breast cancer excess, in fact a non-significant reduction. Long-term follow-up 4 consolidated the picture. The WHI is universally cited but is not a randomized test of bioidentical progesterone vs synthetic progestin; it used MPA throughout.

Observational evidence on the bioidentical-vs-synthetic distinction is dominated by the E3N French cohort. Fournier 2008 6 reported that, compared with never-users, estrogen-plus-progesterone HRT was not associated with an increased breast-cancer risk over 8 years of follow-up, while estrogen plus synthetic progestins (including MPA and norethisterone) was. This observational signal is supportive but not equivalent to randomized evidence; it is cited by NAMS 11 and by the Endocrine Society 10 as informing the rationale for considering micronized progesterone over synthetic progestins in combined HRT.

The preterm-birth program developed across two decades. Da Fonseca 2003 18 reported reduction in spontaneous preterm birth with vaginal progesterone suppositories in women at increased risk. Meis 2003 19 reported large benefit with 17-α-hydroxyprogesterone caproate (17-OHPC) IM in women with prior preterm birth, leading to FDA accelerated approval of Makena. Fonseca 2007 20 and Hassan 2011 21 established benefit of vaginal progesterone specifically in women with a sonographic short cervix. Norman OPPTIMUM 2016 22 failed to replicate broad benefit in a heterogeneous-risk UK trial. The Romero 2018 IPD meta-analysis 23 and the EPPPIC 2021 IPD meta-analysis 24 consolidated the field: vaginal progesterone reduces preterm birth in women with a short cervix; 17-OHPC failed confirmatory replication in PROLONG 25 and Makena was withdrawn from the US market in 2023.

Allopregnanolone biology was developed across the 1990s and 2000s by Majewska, Belelli, Lambert, and others, with foundational reviews by Schumacher 35 and Guennoun 36. The FDA approvals of brexanolone (IV allopregnanolone, 2019) for postpartum depression on the basis of Meltzer-Brody's phase 3 program 34 and the oral allopregnanolone analog zuranolone (2023) clinically validated the GABA-A neurosteroid mechanism. The ProTECT III trial of progesterone for traumatic brain injury 33 was negative, ending an active translational hypothesis.

Compounded bioidentical hormone therapy, including compounded progesterone, was the subject of the 2020 NASEM report 12, which acknowledged legitimate compounding for documented patient-specific need while explicitly criticizing routine substitution of compounded for FDA-approved products without clinical rationale, and explicitly criticizing transdermal progesterone creams marketed for endometrial protection. NAMS 2022 11 and Endocrine Society 2015 10 echo this scope.

Timeline

Progesterone Timeline

  1. 1934 Progesterone isolated and characterized by Butenandt, Slotta, Hartmann, and others in rapid succession; total synthesis from cholesterol follows
  2. 1989 Hargrove and Maxson demonstrate that micronization plus oil vehicle substantially improves oral progesterone absorption, the pharmaceutical basis for modern oral bioidentical progesterone 13
  3. 1996 PEPI (Postmenopausal Estrogen/Progestin Interventions) endometrial-histology paper published, oral micronized progesterone 200 mg cyclic 12 days/month protects estrogen-primed endometrium at a rate equivalent to MPA 1
  4. 1997 Crinone (vaginal progesterone gel) FDA-approved for luteal support and secondary amenorrhea; De Ziegler and Bulletti publish 'The first uterine pass effect' establishing preferential uterine delivery after vaginal administration 15
  5. 1998 Prometrium (oral micronized progesterone in peanut oil) FDA-approved for endometrial protection in combined HRT and for secondary amenorrhea; Cicinelli publishes uterine-artery vs radial-artery progesterone gradient confirming uterine-targeted delivery via vaginal route 16
  6. 2000 Mulac-Jericevic publishes Science paper on PR-B isoform-selective knockout mouse, demonstrates separate-of-function reproductive phenotypes of PR-A and PR-B 37
  7. 2001 Conneely reviews the lessons of progesterone receptor knockout mice, A vs B isoform-selective biology, in Steroids; Wyatt publishes systematic review concluding progesterone/progestogens are not efficacious for PMS 3843
  8. 2002 Women's Health Initiative combined estrogen-plus-MPA arm (Rossouw, JAMA) stopped early for excess CV events, breast cancer, and VTE 2
  9. 2003 Schindler publishes classification and pharmacology of progestins; Meis publishes 17-OHPC trial in NEJM showing reduction in recurrent preterm birth (basis for FDA approval of Makena, later withdrawn); Da Fonseca publishes vaginal progesterone suppository trial showing reduction in preterm birth in women at increased risk 401918
  10. 2006 WHI estrogen-only (CEE) arm in hysterectomized women published (Stefanick et al, JAMA), no breast cancer excess and a non-significant reduction; supports the interpretation that the progestogen component of combined HRT was responsible for much of the breast signal in the combined arm 3
  11. 2007 Endometrin (vaginal insert) FDA-approved for luteal support in ART; Fonseca publishes 'Progesterone and the risk of preterm birth among women with a short cervix' in NEJM, vaginal progesterone reduces preterm birth in women with sonographic short cervix 20
  12. 2008 Fournier publishes the E3N cohort analysis showing estrogen-plus-progesterone HRT carries a smaller breast-cancer signal than estrogen-plus-synthetic-progestin HRT, the principal observational evidence for the bioidentical-vs-synthetic distinction in HRT 6
  13. 2011 Hassan publishes the PREGNANT trial, vaginal progesterone reduces preterm birth in women with a sonographic short cervix in a multicenter randomized double-blind placebo-controlled trial; Caufriez publishes randomized trial of oral progesterone in postmenopausal women showing improvement in sleep architecture and modulation of GH/TSH/melatonin; van der Linden publishes Cochrane review of luteal phase support in ART 213017
  14. 2012 Herzog publishes randomized trial of progesterone in women with epilepsy, overall negative, with a pre-specified subgroup of perimenstrually-exacerbated catamenial epilepsy showing benefit; Hitchcock and Prior publish placebo-controlled randomized trial of oral micronized progesterone for vasomotor symptoms; Ford publishes Cochrane review concluding progesterone is not effective for PMS 312844
  15. 2013 Stanczyk publishes 'Progestogens used in postmenopausal hormone therapy: differences in their pharmacological properties, intracellular actions, and clinical effects', the standard reference for the pharmacology of progestogen heterogeneity; Dodd publishes Cochrane review of antenatal progesterone for preterm birth prevention 3926
  16. 2014 Schumacher publishes 'Revisiting the roles of progesterone and allopregnanolone in the nervous system' (Prog Neurobiol); Herzog publishes follow-up showing allopregnanolone levels track seizure frequency in progesterone-treated women with epilepsy; Wright publishes ProTECT III in NEJM, IV progesterone for severe traumatic brain injury, negative 353233
  17. 2015 Endocrine Society Clinical Practice Guideline on Treatment of Symptoms of the Menopause (Stuenkel et al, JCEM), frames micronized progesterone as a reasonable option for endometrial protection in combined HRT; Guennoun publishes review on progesterone and allopregnanolone CNS effects in J Steroid Biochem Mol Biol 1036
  18. 2016 Norman publishes the OPPTIMUM trial (Lancet), vaginal progesterone for preterm birth prophylaxis in heterogeneous-risk women, primary endpoint negative; Hodis publishes ELITE (NEJM), early postmenopausal oral estradiol plus vaginal progesterone reduced subclinical atherosclerosis vs placebo, while late initiation did not 227
  19. 2017 Manson publishes long-term WHI mortality follow-up (JAMA), no increase in all-cause or cause-specific mortality through 18 years of cumulative follow-up; Hembree publishes updated Endocrine Society guideline on endocrine treatment of gender-dysphoric/gender-incongruent persons (JCEM) 445
  20. 2018 Romero publishes the individual-patient-data meta-analysis of vaginal progesterone for preterm birth prevention in women with a sonographic short cervix, confirms efficacy in the short-cervix subgroup; Meltzer-Brody publishes brexanolone (IV allopregnanolone) phase 3 program in Lancet, clinical proof of GABAergic-neurosteroid mechanism 2334
  21. 2019 Coomarasamy publishes PRISM (NEJM), vaginal progesterone for women with bleeding in early pregnancy, no overall effect on live birth, possible benefit in subgroup with prior miscarriages; FDA approves brexanolone (Zulresso) for postpartum depression 2734
  22. 2020 Blackwell publishes PROLONG (Am J Perinatol), confirmatory phase 4 trial of 17-OHPC for recurrent preterm birth in singletons, negative, failed to replicate Meis 2003; NASEM publishes report on compounded bioidentical hormone therapy 2512
  23. 2021 EPPPIC group publishes individual-patient-data meta-analysis (Lancet) of vaginal progesterone, 17-OHPC, and oral progesterone across the preterm-birth prevention literature, vaginal progesterone confirmed effective in women with short cervix or prior preterm birth; oral progesterone and 17-OHPC not supported 24
  24. 2022 NAMS publishes the 2022 hormone therapy position statement; Coleman publishes WPATH Standards of Care Version 8, both reference micronized progesterone within their respective frameworks 1146
  25. 2023 FDA initiates withdrawal of Makena (17-OHPC) from the US market after PROLONG confirmatory trial failure; vaginal progesterone retains evidence and labeling for short-cervix indication via Crinone and via individual prescription; Prior publishes a phase 3 Canada-wide randomized placebo-controlled 4-month trial of oral micronized progesterone for perimenopausal night sweats and hot flushes 2529

Natural role

Biological Role of Progesterone

Progesterone has three principal physiologic roles in adult women 35. First, it is the luteal-phase hormone of the menstrual cycle: after ovulation, the corpus luteum secretes 20, 25 mg/day at peak, transforming estrogen-primed endometrium into a receptive secretory phase that supports implantation if it occurs. Withdrawal of progesterone (corpus luteum involution if no pregnancy) triggers menstrual sloughing. Second, it is the pregnancy hormone: placental progesterone production rises from milligrams per day in early pregnancy to several hundred milligrams per day at term, maintaining uterine quiescence, immunologic tolerance of the fetus, and decidual integrity. Third, it is a continuous low-level neurosteroid precursor and adrenal-derived contributor in both sexes.

In men and in non-cycling women (prepubertal, postmenopausal, or amenorrheic), basal progesterone concentrations are low, adrenal-derived at approximately 0.1, 0.3 ng/mL, and the principal physiologic role is as substrate for neurosteroid synthesis (allopregnanolone), corticosteroid biosynthesis (progesterone is the immediate precursor of 11-deoxycorticosterone in the mineralocorticoid pathway), and the broader steroidogenic cascade 35.

Endogenous progesterone declines abruptly at menopause (in the year or two surrounding ovarian senescence) alongside the more gradually declining estradiol. Perimenopausal progesterone deficiency is one of the proposed mechanisms underlying perimenopausal sleep disruption, mood lability, and vasomotor symptoms, and is the conceptual basis for off-label perimenopausal progesterone use 30 28 35.

Clinical contexts studied

Clinical Contexts for Progesterone

Endometrial protection in estrogen-containing menopausal hormone therapy fda approved

FDA-approved indication for oral micronized progesterone (Prometrium); foundational evidence from PEPI.

Oral micronized progesterone is FDA-approved for the prevention of endometrial hyperplasia and adenocarcinoma in postmenopausal women with an intact uterus who are receiving estrogen therapy. The PEPI trial 1 established that micronized progesterone 200 mg cyclic for 12 days each month protects estrogen-primed endometrium at a rate equivalent to medroxyprogesterone acetate, with markedly lower hyperplasia rates than estrogen alone. Continuous-combined regimens use lower daily doses (typically 100 mg/day) with similar endometrial protection. NAMS 11 and the Endocrine Society 10 support micronized progesterone as the bioidentical option in this indication, with the additional consideration from the E3N cohort 6 that bioidentical progesterone may carry a smaller breast-cancer signal than synthetic progestins.

Branded product: Prometrium

Luteal support in assisted reproductive technology fda approved

FDA-approved indication for vaginal progesterone (Crinone, Endometrin); supported by Cochrane meta-analysis.

Vaginal progesterone, gel (Crinone 8%) or insert (Endometrin 100 mg), is FDA-approved for luteal-phase support in women undergoing assisted reproductive technology (IVF/ICSI). Vaginal administration exploits the first uterine pass effect 15 16 to deliver progesterone preferentially to the uterus. The Cochrane review by van der Linden 17 confirms benefit on clinical pregnancy and ongoing pregnancy outcomes vs no support. IM progesterone in oil and oral micronized progesterone are alternative routes used in some protocols; vaginal is the most-used route in current US ART practice.

Branded product: Crinone, Endometrin

Secondary amenorrhea fda approved

FDA-approved for inducing withdrawal bleeding in non-pregnant women with secondary amenorrhea and estrogen-primed endometrium.

Oral micronized progesterone (Prometrium) 400 mg/day for 10 days induces a withdrawal bleed in non-pregnant women with secondary amenorrhea and adequate endogenous estrogen, the 'progesterone challenge test' in its diagnostic use, and a short course for inducing menstrual cyclicity in its therapeutic use 10.

Branded product: Prometrium

Prevention of preterm birth in women with a short cervix well studied

Well-studied; vaginal progesterone has the strongest evidence in the short-cervix subgroup.

Vaginal progesterone (200 mg/day suppository, or 90 mg gel) reduces spontaneous preterm birth in women with a sonographic short cervix (typically defined as ≤25 mm in the mid-trimester) 18. The Fonseca 2007 20 and Hassan 2011 21 RCTs are the foundational randomized evidence; the Romero 2018 individual-patient-data meta-analysis 23 and the EPPPIC 2021 IPD meta-analysis 24 consolidated the short-cervix benefit across the trial program. Norman OPPTIMUM 2016 22 was negative in a heterogeneous-risk UK population (its primary endpoint was a composite; the short-cervix subgroup was small). 17-OHPC IM (Makena), positive in Meis 2003 19, failed confirmatory replication in PROLONG 2020 25 and was withdrawn from the US market in 2023.

Endometrial hyperplasia treatment (off-label) and bioidentical-vs-synthetic considerations well studied

Well-studied bioidentical-vs-synthetic distinction; endometrial protection is the foundational evidence base for the comparison.

PEPI 1 established that oral micronized progesterone protects estrogen-primed endometrium at a rate equivalent to MPA 41. WHI 2 3 4 used MPA, not micronized progesterone, throughout; its breast and cardiovascular signals cannot be cleanly attributed to either the estrogen or the progestogen component. The E3N cohort 6 is the principal observational evidence that estrogen-plus-bioidentical-progesterone may carry a smaller breast-cancer signal than estrogen-plus-synthetic-progestin combined HRT 39. NAMS 2022 11, the Endocrine Society 2015 10, and NASEM 2020 12 frame this as informing choice of progestogen in combined HRT, while noting the lack of head-to-head randomized data.

Cardiovascular safety of combined HRT including progesterone well studied

Well-studied; ELITE provides randomized evidence on early-vs-late initiation.

The cardiovascular signal from WHI 2 in women a decade or more past menopause produced a generation of caution about combined HRT. The KEEPS 8 and ELITE 7 trials addressed the 'timing hypothesis', that initiation closer to the menopause transition might produce different cardiovascular outcomes. ELITE in particular randomized 643 postmenopausal women to oral estradiol plus cyclic vaginal progesterone vs placebo and found reduced progression of carotid intima-media thickness when therapy was initiated within 6 years of menopause but not when initiated 10+ years out 4. KEEPS-Cog 9 examined cognitive outcomes. Neither trial was powered for hard CV events.

Catamenial epilepsy well studied

Off-label; randomized evidence supports subgroup with perimenstrually-exacerbated seizures.

Catamenial epilepsy, seizures clustered around the perimenstrual or periovulatory phases of the cycle, is mechanistically linked to fluctuations in allopregnanolone, the GABA-A-modulating progesterone metabolite 35 36. The Herzog 2012 NIH-sponsored RCT 31 was overall negative for unselected women with epilepsy but pre-specified a perimenstrually-exacerbated catamenial subgroup that showed benefit. Herzog 2014 32 showed that allopregnanolone levels track seizure reduction, supporting the mechanism. Progesterone is not a first-line antiseizure drug; this is a specialty neurology indication.

Perimenopausal vasomotor symptoms well studied

Off-label; modest randomized evidence supports a role.

Hitchcock and Prior's 2012 placebo-controlled RCT 28 of oral micronized progesterone 300 mg at bedtime in healthy postmenopausal women showed reduction in vasomotor symptom severity vs placebo, without rebound on discontinuation. Prior's 2023 phase 3 Canada-wide RCT 29 in perimenopausal women supported night sweat reduction. NAMS 2022 11 does not list progesterone monotherapy as a first-line VMS therapy but acknowledges the evidence base.

Sleep disturbance in perimenopause and postmenopause well studied

Off-label; modest randomized evidence for bedtime oral progesterone.

Caufriez 2011 30 randomized 8 postmenopausal women in a crossover trial of oral micronized progesterone 300 mg vs placebo at bedtime and showed improved sleep architecture (reduced wake after sleep onset) along with modulation of GH, TSH, and melatonin. The sleep benefit is mechanistically attributed to allopregnanolone's GABA-A action 35. This is the basis for the recommendation that oral progesterone be dosed at bedtime in combined HRT regimens, converting somnolence from an adverse effect into a therapeutic effect 36.

Off-label use

Off-Label Uses of Progesterone

Premenstrual syndrome / premenstrual dysphoric disorder emerging

Not supported by Cochrane review or systematic review, efficacy not established.

Wyatt 2001 43 systematic review and the Ford 2012 Cochrane review 44 concluded that neither progesterone nor synthetic progestogens are effective for PMS. Despite continued prescribing in some practice settings, the evidence does not support efficacy. SSRIs, dietary measures, and ovulation suppression have stronger evidence bases for PMDD.

First-trimester threatened miscarriage well studied

Off-label; PRISM 2019 was overall negative with a possible subgroup signal.

The PRISM trial 27 randomized 4153 women with bleeding in early pregnancy to vaginal micronized progesterone 400 mg BID or placebo. The primary endpoint (live birth ≥34 weeks) showed no significant overall benefit. A pre-specified subgroup analysis suggested benefit in women with prior miscarriages, with effect size increasing with number of prior losses. The trial does not support routine progesterone for unselected early-pregnancy bleeding but is part of the rationale some clinicians cite for selective use in recurrent pregnancy loss.

Recurrent preterm birth (singleton, prior preterm birth) well studied

17-OHPC (Makena) withdrawn from market 2023 after PROLONG confirmatory trial failure; vaginal progesterone retains evidence.

Meis 2003 19 reported reduction in recurrent preterm birth with weekly IM 17-α-hydroxyprogesterone caproate in women with a prior preterm birth, leading to FDA accelerated approval of Makena. PROLONG 2020 25 was the FDA-required confirmatory trial and was negative. Makena was withdrawn from the US market in 2023. Vaginal micronized progesterone for women with both prior preterm birth and a short cervix retains evidence per the EPPPIC IPD meta-analysis 24 26.

Gender-affirming feminizing hormone therapy emerging

Limited evidence; not routinely included in major guidelines.

Some clinicians add bioidentical progesterone to feminizing hormone therapy regimens (estradiol ± anti-androgen) with the goals of breast development, mood support, libido modulation, and sleep. Evidence is limited and the Endocrine Society 2017 guideline 45 does not include progesterone as standard, while WPATH SOC 8 46 acknowledges its use within shared decision-making frameworks. RonanRx compounds bioidentical progesterone in this context only on a patient-specific prescription from a knowledgeable clinician.

Traumatic brain injury preclinical

ProTECT III was negative, no clinical indication.

Decades of preclinical data suggested neuroprotective effects of progesterone after TBI. The ProTECT III randomized trial 33 of IV progesterone in severe TBI was negative; a parallel European trial (SyNAPSe) was also negative. There is no clinical indication for progesterone in TBI.

Postpartum depression fda approved

Bioidentical oral progesterone is not the validated mechanism; IV allopregnanolone (brexanolone) is FDA-approved.

Allopregnanolone, the GABA-A-modulating metabolite of progesterone, is the validated mechanism for postpartum depression treatment. IV brexanolone (Zulresso) was FDA-approved in 2019 on the basis of Meltzer-Brody's phase 3 program 34. Oral allopregnanolone analog zuranolone followed in 2023. Oral bioidentical progesterone itself has not been shown effective for postpartum depression in randomized trials; the brexanolone evidence supports the mechanism, not the use of oral progesterone for this indication. This is the clearest clinical proof that the neurosteroid pathway distinguishes bioidentical progesterone from synthetic progestins (which do not reliably generate allopregnanolone) 3536.

FDA-approved use

FDA-Approved Uses of Progesterone

BrandIndicationYearRoute
Prometrium Endometrial protection in postmenopausal women receiving estrogen; secondary amenorrhea 1998 Oral (micronized progesterone in peanut oil)
Crinone Luteal support in assisted reproductive technology; secondary amenorrhea 1997 Vaginal gel (4% and 8%)
Endometrin Luteal support in assisted reproductive technology 2007 Vaginal insert (100 mg)
Progesterone in oil (generic) Luteal support in ART; secondary amenorrhea Pre-1962 / grandfathered Intramuscular (progesterone in sesame or other oil)

Three principal FDA-approved manufactured products contain bioidentical progesterone: Prometrium (oral micronized in peanut oil, 1998), Crinone (vaginal gel, 1997), and Endometrin (vaginal insert, 2007). Generic intramuscular progesterone in oil has been in clinical use since before the modern FDA approval framework 10. 17-α-hydroxyprogesterone caproate (Makena), which is not bioidentical progesterone but a chemically distinct 17-OH-progesterone caproate ester, was withdrawn from the US market in 2023 after the PROLONG confirmatory trial 25 failed to replicate the Meis 2003 19 preterm-birth-prevention benefit.

Each FDA-approved product is indicated for narrow specific use: Prometrium for endometrial protection in combined HRT and for secondary amenorrhea, Crinone/Endometrin for luteal support in ART 117. Crinone also has a labeling indication for secondary amenorrhea. Use of these products for vaginal preterm-birth prevention, perimenopausal vasomotor symptoms, sleep, catamenial epilepsy, or other off-label indications relies on the published evidence summarized in clinical_contexts and off_label_uses 1011.

Compounded use

Compounded Progesterone (503A)

Compounded bioidentical progesterone occupies a circumscribed but legitimate role under 503A 47. The manufactured market provides Prometrium at 100 mg and 200 mg only, Crinone at 4% and 8% only, and Endometrin at 100 mg only. Patient-specific compounding addresses needs the manufactured market does not, intermediate oral strengths (50 mg, 75 mg, 150 mg) for titration, troche dosage forms for patients who cannot tolerate the peanut-oil excipient in Prometrium (peanut allergy is the most common reason), vaginal suppositories at strengths or in vehicles not available manufactured, and rectal suppositories in select clinical scenarios. The NASEM 2020 report 12 is the consensus document on this scope.

RonanRx is explicit about one specific limitation: compounded transdermal progesterone creams produce serum levels that are inadequate to reliably oppose estrogen-induced endometrial proliferation 47. They should not be used as the progestogen arm of a combined estrogen-plus-progestogen regimen for endometrial protection. NASEM 2020 12, NAMS 2022 11, and the Endocrine Society 2015 10 all flag this point. Compounded creams may be appropriate in specific, documented patient-specific scenarios that do not depend on serum-level-mediated endometrial action, but as endometrial-protection therapy they are not adequate.

Routine substitution of compounded oral progesterone for Prometrium without a documented clinical reason (such as peanut-oil allergy, need for a non-100/200 mg strength, or a documented excipient sensitivity) is not consistent with FDA guidance on compounded copies of approved drugs 48. RonanRx's pharmacist review documents the patient-specific clinical reason for each compounded prescription 47.

Formulations and routes

Progesterone Formulations and Routes

FormConcentrationDescription
Oral micronized progesterone capsule (compounded) Custom, typical 25, 50, 75, 100, 150, 200 mg Bioidentical micronized progesterone in oil (often olive, MCT, or other oils as alternatives to the peanut-oil excipient in manufactured Prometrium). Indicated for patients with peanut-oil sensitivity, those needing strengths between or outside the manufactured 100/200 mg range, or those requiring excipient substitution.13
Oral progesterone troche / sublingual lozenge (compounded) Custom, typical 25, 100 mg per troche Slow-dissolve buccal/sublingual troche. Partially bypasses first-pass hepatic metabolism. Often selected for patients with GI absorption concerns or peanut-oil sensitivity. Pharmacokinetics differ from oral capsule, serum profile is more pulsatile.
Vaginal progesterone suppository (compounded) Custom, typical 100, 200, 400 mg Compounded suppositories in polyethylene glycol, cocoa butter, or other vehicles. Used for luteal support, endometrial protection (when oral route is not tolerated), and at 200 mg/day for preterm birth prevention in women with short cervix [hassan2011shortcervix]. Vaginal route exploits the first uterine pass effect [deziegler1997firstpass] for preferential uterine delivery.1521
Rectal progesterone suppository (compounded) Custom, typical 100, 400 mg Alternative route for select clinical scenarios when neither oral nor vaginal route is appropriate. Less first-pass than oral; less uterine-targeted than vaginal.
Transdermal / topical progesterone cream (compounded) Custom, typical 20, 100 mg per gram Topical cream for application to skin. Inadequate for endometrial protection in combined estrogen HRT regimens; serum levels do not reliably reach the threshold associated with secretory transformation of estrogen-primed endometrium [nasem2020bht]. May be appropriate for narrow, documented patient-specific scenarios that do not depend on serum-level-mediated systemic effect.121011
Intramuscular progesterone in oil 50 mg/mL standard manufactured strength; custom strengths compounded Progesterone in sesame, cottonseed, or other oil vehicle for IM injection. Used principally for luteal support in ART. Custom strengths or alternative-oil compounding addresses sesame-oil sensitivity.

Routes used in published literature: oral, vaginal, rectal, intramuscular, topical, transdermal, sublingual, troche.

Dosing

Progesterone Dosing

RoutePopulationRangeDurationStudy type
Oral Postmenopausal women on combined HRT, endometrial protection 100 mg at bedtime daily (continuous-combined regimen) OR 200 mg at bedtime for 12 days each month (cyclic-sequential regimen) Indefinite while clinically beneficial; reassess periodically per NAMS 2022 and Endocrine Society 2015 PEPI randomized trial; NAMS 2022 position statement; Endocrine Society 2015 guideline11110
Oral Adult women, secondary amenorrhea (induction of withdrawal bleed) 400 mg/day for 10 days 10 days Prometrium labeled regimen10
Vaginal (gel, Crinone) ART luteal support 90 mg (Crinone 8%) once daily; in some protocols once or twice daily depending on fresh vs frozen-embryo cycle From oocyte retrieval through ~10 weeks gestation if pregnancy occurs, then physician-directed taper FDA-labeled regimen; Cochrane review by van der Linden 201117
Vaginal (insert, Endometrin) ART luteal support 100 mg vaginal insert two or three times daily From oocyte retrieval through ~10 weeks gestation if pregnancy occurs FDA-labeled regimen17
Vaginal (compounded suppository) Pregnant women with sonographic short cervix (≤25 mm in mid-trimester), preterm birth prevention 200 mg vaginally at bedtime daily From identification of short cervix through 36 0/7 weeks gestation or delivery Hassan 2011 PREGNANT trial; Romero 2018 IPD meta-analysis; EPPPIC 2021 IPD meta-analysis21232420
Intramuscular (progesterone in oil) ART luteal support 50, 100 mg IM daily From oocyte retrieval through ~10 weeks gestation Long-standing ART protocol; Cochrane review by van der Linden 201117
Oral (off-label) Perimenopausal women, vasomotor symptoms 300 mg at bedtime daily (Hitchcock 2012 trial regimen) 3, 4 months trial; reassess Hitchcock 2012 placebo-controlled RCT; Prior 2023 Canada-wide phase 3 RCT2829
Oral (off-label) Women with catamenial epilepsy, perimenstrual exacerbation subgroup 200 mg three times daily during luteal phase (Herzog 2012 trial regimen, cycle days 14, 28 with taper) Cycle-locked; reassess at 3 months Herzog 2012 NIH-sponsored RCT, overall negative, perimenstrually-exacerbated subgroup positive3132

Doses listed reflect FDA-labeled regimens and published clinical-trial protocols, not RonanRx prescribing recommendations 11. The prescribing clinician selects formulation, route, and dose based on indication, clinical context, prior tolerability, and shared decision-making.

Practical considerations: oral micronized progesterone is dosed at bedtime to use the somnolence effect therapeutically rather than as an adverse effect, and because the allopregnanolone surge after oral absorption peaks within 1, 4 hours, a window that overlaps natural sleep latency 35. Vaginal progesterone produces lower serum levels than oral or IM at comparable doses but concentrates in the uterus via the first uterine pass effect 15, making vaginal the route of choice when uterine action is the goal (luteal support, endometrial protection in women with adequate vaginal absorption, short-cervix prophylaxis) 1. IM progesterone produces high stable serum levels but is uncomfortable and is generally reserved for ART protocols where vaginal route is contraindicated or inadequate. Transdermal cream is inadequate for endometrial protection, this is a guideline-level point, not an opinion 12 10.

Combined HRT regimen choice: continuous-combined estrogen + progesterone 100 mg/day produces amenorrhea after a transition period and is preferred by most postmenopausal women 1. Cyclic-sequential estrogen + progesterone 200 mg × 12 days/month produces a withdrawal bleed each cycle and is sometimes preferred by women in early postmenopause or those who prefer a predictable bleed pattern 11.

Doses listed are literature context, not patient instructions. Dosing decisions are made by the prescribing doctor and tailored to the individual patient.

Safety

Progesterone Safety

Safety overview

Bioidentical progesterone has a favorable safety profile relative to synthetic progestins, with the most common on-therapy effects being dose-dependent somnolence and mild dizziness after oral dosing (an allopregnanolone-mediated GABA-A effect) 35. Bedtime dosing converts somnolence from an adverse effect into a therapeutic effect. Mood lability, breast tenderness, and bloating are also reported.

Cardiovascular and breast safety: the WHI 2 3 used medroxyprogesterone acetate, not bioidentical progesterone, and its breast and CV signals cannot be cleanly attributed to either component. The E3N observational cohort 6 reported a smaller breast-cancer signal with estrogen-plus-bioidentical-progesterone than with estrogen-plus-synthetic-progestin combined HRT. Randomized head-to-head comparison of bioidentical vs synthetic progestogen for breast safety in combined HRT does not exist. NAMS 2022 11, the Endocrine Society 2015 10, and the NASEM 2020 report 12 frame this distinction as informing choice rather than as a randomized safety claim.

Pregnancy: vaginal and IM progesterone for luteal support in ART and for short-cervix preterm-birth prophylaxis 21 23 have favorable safety profiles in the established randomized literature. No teratogenicity signal is established for bioidentical progesterone at the doses used clinically. 17-α-hydroxyprogesterone caproate (Makena) was withdrawn from market in 2023 after PROLONG failed confirmatory replication, but vaginal progesterone retains evidence 24 25.

Transdermal cream-specific caution: progesterone creams do not produce serum levels adequate to oppose estrogen-induced endometrial proliferation. They are not appropriate as the progestogen arm of combined estrogen HRT for women with an intact uterus 12 10.

Contraindications

Bioidentical progesterone (oral, vaginal, IM, or compounded) is contraindicated in: known hypersensitivity to progesterone or formulation excipients (Prometrium contains peanut oil, peanut allergy is a contraindication to that specific manufactured product; compounded preparations in alternative oils address this); known or suspected breast cancer (relative, discuss with oncology); active thrombophlebitis or thromboembolic disorders; cerebrovascular disease; severe hepatic impairment; undiagnosed abnormal genital bleeding; known or suspected pregnancy when not being used specifically to support pregnancy (e.g., not appropriate as menopausal HT when pregnancy is possible); missed abortion as a diagnostic test of choice (use other methods).

Relative cautions per NAMS 2022 11 and Endocrine Society 2015 10: prior personal history of breast cancer (oncology-shared decision-making), prior personal history of VTE or known thrombophilia (oral progesterone has minimal VTE signal compared with synthetic progestins; route choice matters), and active liver disease.

Transdermal cream is contraindicated as the sole progestogen arm of combined estrogen HRT in women with an intact uterus, because serum levels are inadequate for endometrial protection 12.

Drug interactions

Progesterone is metabolized primarily by CYP3A4 in the liver. Strong CYP3A4 inducers (rifampin, carbamazepine, phenytoin, St John's wort) can lower serum progesterone concentrations; strong CYP3A4 inhibitors (ketoconazole, itraconazole, ritonavir, clarithromycin, grapefruit juice in large quantities) can raise them. In women on combined HRT, this can affect the adequacy of endometrial protection. In women using progesterone for catamenial epilepsy, concomitant enzyme-inducing antiepileptics can reduce the allopregnanolone-mediated benefit 32 35.

CNS-depressant drugs (benzodiazepines, opioids, alcohol, sedating antihistamines) may have additive effects with the allopregnanolone-mediated sedation of oral progesterone, particularly relevant for the bedtime dosing common in combined HRT 35. Patients should be counseled about additive sedation if combining 10.

Adverse events

The most common on-therapy adverse events of oral micronized progesterone are dose-dependent somnolence and mild dizziness (allopregnanolone GABA-A effect) 35. Bedtime dosing makes these therapeutic rather than burdensome. Breast tenderness, mild bloating, mood lability, and headache are also reported. Vaginal preparations produce local effects: vaginal discharge, itching, and burning are most common; partner exposure during intercourse is generally minimal in clinical reports. IM progesterone in oil produces local injection-site pain, occasional sterile abscess, and rare allergic reactions to the oil vehicle.

Pregnancy-related: in the large randomized vaginal-progesterone preterm-birth trials 21 22 23 24, safety signals were limited to local vaginal effects without an established teratogenic, neonatal, or long-term developmental signal at the doses studied. The PROLONG trial of 17-OHPC 25 (a different molecule from bioidentical progesterone) showed no efficacy signal but also no major safety signal.

Site-specific adverse events vary by route: oral, somnolence, dizziness, headache, breast tenderness; vaginal, local irritation, discharge; IM, injection-site pain, oil-vehicle local reactions; transdermal cream, minimal systemic effects (consistent with the inadequate serum levels that also make it inadequate for endometrial protection 12).

Monitoring

Monitoring Progesterone Therapy

Combined HRT monitoring per NAMS 2022 11 and Endocrine Society 2015 10: baseline review of indications, contraindications, breast and endometrial cancer risk factors; periodic reassessment of indication, dose, and route at least annually; investigation of any abnormal uterine bleeding on a regimen designed to produce amenorrhea (continuous-combined) or unexpected bleeding pattern on a cyclic regimen. Mammography and breast clinical exam per age-appropriate screening guidelines. Serum progesterone levels are not routinely used to titrate menopausal HT, the clinical endpoint is symptom control and absence of abnormal bleeding 21.

ART luteal support: monitoring is for the pregnancy outcome, not for serum progesterone level. Most US protocols use vaginal or IM progesterone through ~10 weeks gestation, then taper 21.

Short-cervix preterm-birth prophylaxis: vaginal progesterone 200 mg nightly from identification of short cervix through 36 0/7 weeks 21. Ultrasound follow-up for cervical length and obstetric monitoring per OB protocols.

Catamenial epilepsy: cycle-locked dosing requires careful menstrual cycle tracking; allopregnanolone level monitoring is research-grade not routine 32; seizure frequency is the clinical endpoint 21.

Special populations

Progesterone in Special Populations

Pregnancy

Bioidentical progesterone has FDA approval for use in pregnancy in the ART luteal-support indication (Crinone, Endometrin) 17. Vaginal progesterone for prevention of preterm birth in women with a sonographic short cervix 21 23 24 is widely used in obstetric practice. The randomized literature does not establish a teratogenic, neonatal, or developmental signal at the doses used clinically.

Compounded progesterone preparations dispensed in pregnancy follow the same patient-specific 503A framework. RonanRx dispenses compounded vaginal suppositories for short-cervix prophylaxis or for luteal support only on a patient-specific prescription from the obstetrician or REI specialist 17.

Lactation

Limited progesterone passes into breast milk and no clinical concern is established for breastfeeding infants at the doses used in combined HRT or in postpartum settings. Brexanolone (IV allopregnanolone for postpartum depression) has its own labeling 34.

Pediatric

Not generally indicated in pediatric populations outside of specialty endocrinology contexts (e.g., delayed puberty management in specific endocrine syndromes). Not addressed in detail on this page.

Geriatric

Use in postmenopausal women is the principal context. The NAMS 2022 11 and Endocrine Society 2015 10 position statements address geriatric considerations including the timing hypothesis, that initiation of combined HRT closer to the menopause transition produces different cardiovascular outcomes than late initiation (ELITE 7; WHI long-term follow-up 4). Annual review of indication, dose, and route is standard.

Hepatic impairment

Progesterone is hepatically metabolized; severe hepatic impairment is a contraindication to oral therapy. Vaginal or IM routes may be considered when liver function is marginal but oral is contraindicated; specialty consultation advised 10.

Evidence quality

Progesterone Evidence Quality

Evidence for bioidentical progesterone is anchored by three randomized programs and one large observational cohort 29. PEPI 1 established endometrial protection equivalence with MPA. The vaginal-progesterone preterm-birth program, Da Fonseca 2003 18, Fonseca 2007 20, Hassan 2011 21, Norman OPPTIMUM 2016 22, Romero 2018 IPD 23, EPPPIC 2021 IPD 24, established benefit in the short-cervix subgroup with negative or null findings in unselected populations. The Cochrane review of luteal support in ART 17 supports the FDA-approved ART use.

The E3N observational cohort 6 is the principal source of the bioidentical-vs-synthetic-progestogen breast-cancer signal. WHI 2 3 4 used MPA and does not directly inform the bioidentical-progesterone safety question. The 'timing hypothesis' randomized trials KEEPS 8 9 and ELITE 7 used micronized progesterone in their combined-HRT arms 29.

Off-label evidence is mixed: positive in perimenopausal vasomotor symptoms 28, positive in sleep 30, positive in a perimenstrually-exacerbated catamenial epilepsy subgroup 31, negative in unselected PMS/PMDD 43, and negative in traumatic brain injury (ProTECT III 33). The brexanolone phase 3 program for postpartum depression 34 is the clinical proof of the allopregnanolone GABA-A mechanism that mechanistically distinguishes bioidentical progesterone from synthetic progestins 44.

The Stanczyk 2013 39, Schindler 2003 40, and Campagnoli 2005 41 reviews are the standard references for progestogen pharmacology and the bioidentical-vs-synthetic distinction 29. Schumacher 2014 35 and Guennoun 2015 36 are the standard references for neurosteroid biology. NAMS 2022 11, Endocrine Society 2015 10, and NASEM 2020 12 are the consensus position statements that frame the clinical role of compounded bioidentical hormone therapy.

Major studies

Major Progesterone Clinical Studies

StudyDesignParticipantsDurationFinding
PEPI, Effects of Hormone Replacement Therapy on Endometrial Histology in Postmenopausal Women (PEPI Writing Group 1996 JAMA) 3-year multicenter randomized placebo-controlled trial, 5 arms including conjugated estrogen plus cyclic micronized progesterone vs estrogen plus MPA vs estrogen alone vs placebo 596 3 years Oral micronized progesterone 200 mg/day for 12 days/month protected estrogen-primed endometrium at a rate equivalent to MPA; both produced rates of hyperplasia indistinguishable from placebo, while estrogen alone produced ~34% hyperplasia 1
WHI, Risks and Benefits of Estrogen Plus Progestin in Healthy Postmenopausal Women (Rossouw 2002 JAMA) Randomized double-blind placebo-controlled trial of CEE + MPA vs placebo in postmenopausal women with intact uterus 16608 Mean 5.2 years (stopped early) Increased coronary heart disease, breast cancer, stroke, and VTE; reduced fractures and colorectal cancer; overall risk-benefit unfavorable in the population studied. Used MPA, not bioidentical progesterone 2.
WHI Estrogen-Only Arm, Effects of CEE on Breast Cancer (Stefanick 2006 JAMA) Randomized trial of CEE alone vs placebo in postmenopausal women with prior hysterectomy 10739 Mean 7.1 years No increase in breast cancer (non-significant reduction); reinforces interpretation that the progestogen (MPA) component of the combined arm contributed substantially to that arm's breast-cancer signal 3
WHI Long-Term Follow-Up, Menopausal Hormone Therapy and All-Cause Mortality (Manson 2017 JAMA) Long-term follow-up of both WHI hormone therapy trials 27347 Cumulative 18 years No significant increase in all-cause, cardiovascular, or cancer mortality over 18-year cumulative follow-up, contextualizes the original 2002 stopping decision 4
HERS, Estrogen Plus Progestin for Secondary Prevention of CHD (Hulley 1998 JAMA) Randomized placebo-controlled secondary-prevention trial in postmenopausal women with established CHD 2763 Mean 4.1 years No overall reduction in CHD events; early increase in events; informed FDA labeling on use in secondary CV prevention 5. Used CEE + MPA.
E3N Cohort, Unequal Risks for Breast Cancer Associated with Different HRTs (Fournier 2008) Prospective cohort of French postmenopausal women Over 80,000 women Mean 8 years follow-up Estrogen plus bioidentical progesterone HRT not associated with increased breast cancer risk vs never-use; estrogen plus synthetic progestins associated with increased risk, principal observational evidence for the bioidentical-vs-synthetic distinction 6
ELITE, Vascular Effects of Early vs Late Postmenopausal Treatment with Estradiol (Hodis 2016 NEJM) Randomized placebo-controlled trial of oral estradiol plus cyclic vaginal progesterone in early vs late postmenopausal women 643 Median 5 years Reduced progression of carotid intima-media thickness in women starting within 6 years of menopause; no effect in women starting 10+ years out, supports the timing hypothesis; used micronized progesterone vaginally 7
KEEPS, Kronos Early Estrogen Prevention Study (Harman 2014) Randomized placebo-controlled trial of oral CEE or transdermal estradiol, each with cyclic oral micronized progesterone, in early postmenopausal women 727 4 years No effect on progression of subclinical atherosclerosis; modest favorable effects on symptoms and some metabolic measures; KEEPS-Cog analyzed cognitive outcomes 89
Da Fonseca 2003, Vaginal Progesterone Suppository for Preterm Birth Prevention Randomized placebo-controlled trial of vaginal progesterone 100 mg/day suppository in women at increased preterm-birth risk 142 From 24 weeks to 34 weeks gestation Reduced spontaneous preterm birth before 37 weeks, foundational early evidence for vaginal progesterone in preterm-birth prophylaxis 18
Meis 2003, 17-OHPC for Recurrent Preterm Birth (NEJM) Randomized placebo-controlled trial of weekly IM 17-α-hydroxyprogesterone caproate in women with prior preterm birth 463 From 16, 20 weeks through 36 weeks gestation Reduced recurrent preterm birth, basis for FDA accelerated approval of Makena; later failed confirmatory replication in PROLONG 19
Fonseca 2007, Progesterone and Risk of Preterm Birth in Women with Short Cervix (NEJM) Randomized placebo-controlled trial of vaginal progesterone 200 mg/day in women with sonographic short cervix 250 From mid-trimester through 34 weeks Reduced spontaneous preterm birth before 34 weeks in women with a short cervix 20
Hassan 2011 PREGNANT, Vaginal Progesterone for Short Cervix Multicenter randomized double-blind placebo-controlled trial of vaginal progesterone gel 90 mg/day in women with sonographic short cervix 458 From 19, 24 weeks through 36 weeks Reduced preterm birth before 33 weeks by 45%; reduced neonatal morbidity 21
Norman OPPTIMUM 2016, Vaginal Progesterone in Heterogeneous-Risk Women (Lancet) UK multicenter randomized placebo-controlled trial of vaginal progesterone 200 mg/day in women at increased preterm-birth risk 1228 From 22, 24 weeks through 34 weeks No significant effect on composite obstetric or neonatal primary outcome; short-cervix subgroup small and underpowered 22
Romero 2018 IPD Meta-Analysis, Vaginal Progesterone for Short Cervix Individual-patient-data meta-analysis of randomized trials of vaginal progesterone in women with sonographic short cervix Approximately 974 women across 5 trials Per-trial Vaginal progesterone reduces preterm birth before 33 weeks and improves neonatal outcomes in women with a sonographic short cervix 23
EPPPIC 2021 IPD Meta-Analysis, Evaluating Progestogens for Preventing Preterm Birth (Lancet) Individual-patient-data meta-analysis spanning vaginal progesterone, 17-OHPC, and oral progesterone trials Approximately 11,644 women across 31 trials Pooled randomized data Vaginal progesterone reduces preterm birth and adverse perinatal outcomes in women with a short cervix or prior preterm birth; 17-OHPC and oral progesterone do not show consistent benefit 24
PROLONG 2020, 17-OHPC Confirmatory Trial (Blackwell, Am J Perinatol) Phase 4 multicenter international randomized placebo-controlled trial 1708 Through 37 weeks No significant effect on preterm birth before 35 weeks or on neonatal morbidity, failed to replicate Meis 2003; basis for FDA withdrawal of Makena in 2023 25
Dodd 2013 Cochrane Review, Antenatal Progesterone for Preterm Birth Prevention Cochrane systematic review and meta-analysis of randomized trials — Pooled randomized data Progesterone reduces preterm birth in selected populations (prior preterm birth, short cervix); route and dose matter 26
Cochrane Luteal Phase Support in ART (van der Linden 2011) Cochrane systematic review of luteal phase support in IVF/ICSI — Pooled randomized data Luteal phase support with progesterone (vaginal, IM, or oral) improves clinical pregnancy and ongoing pregnancy rates 17
PRISM, Progesterone for Bleeding in Early Pregnancy (Coomarasamy 2019 NEJM) Randomized double-blind placebo-controlled trial of vaginal micronized progesterone 400 mg BID 4153 From bleeding to 16 weeks No significant effect on live birth ≥34 weeks overall; subgroup with prior miscarriages showed possible benefit, particularly with ≥3 prior losses 27
Hitchcock 2012, Oral Micronized Progesterone for Vasomotor Symptoms Randomized double-blind placebo-controlled trial of oral progesterone 300 mg at bedtime 133 12 weeks Reduced vasomotor symptom severity vs placebo; no rebound on discontinuation 28
Prior 2023, Oral Micronized Progesterone for Perimenopausal Night Sweats and Hot Flushes Phase 3 Canada-wide multicenter randomized placebo-controlled trial — 4 months Reduced perimenopausal night sweats and hot flushes, extends Hitchcock 2012 evidence to perimenopausal population 29
Caufriez 2011, Progesterone for Sleep in Postmenopausal Women Randomized crossover trial of oral progesterone 300 mg at bedtime vs placebo 8 Per-arm Reduced wakefulness, modulated GH/TSH/melatonin; basis for the recommendation to dose oral progesterone at bedtime 30
Herzog 2012, Progesterone for Catamenial Epilepsy (NIH-Sponsored RCT) Randomized placebo-controlled trial of oral progesterone in women with intractable focal epilepsy 294 3 months Overall negative on the primary endpoint; pre-specified perimenstrually-exacerbated catamenial subgroup showed seizure reduction 31
Herzog 2014, Allopregnanolone Levels in Progesterone-Treated Epilepsy Post-hoc analysis of Herzog 2012 trial — Per-trial Allopregnanolone levels track seizure-frequency reduction, supports the GABA-A neurosteroid mechanism 32
Wright 2014 ProTECT III, Progesterone for Severe Traumatic Brain Injury (NEJM) Randomized placebo-controlled trial of IV progesterone in severe TBI 882 30 days to 6 months No significant effect on Glasgow Outcome Scale-Extended at 6 months; ended an active translational hypothesis 33
Meltzer-Brody 2018, Brexanolone (IV Allopregnanolone) for Postpartum Depression (Lancet) Two multicenter phase 3 randomized placebo-controlled trials Approximately 246 women across both trials 60-hour IV infusion with follow-up to 30 days Significant reduction in Hamilton Depression Rating Scale at 60 hours and 30 days; basis for FDA approval (2019), clinical proof of GABAergic-neurosteroid mechanism that distinguishes bioidentical progesterone from synthetic progestins 34
Wyatt 2001, Progesterone for PMS (BMJ Systematic Review) Systematic review of randomized trials of progesterone and progestogens in PMS — Pooled randomized data No evidence of efficacy of progesterone or progestogens for PMS 43
Ford 2012, Progesterone for PMS (Cochrane Review) Cochrane systematic review of randomized trials — Pooled randomized data Insufficient evidence to support progesterone for PMS; SSRIs and other approaches preferred 44
Mulac-Jericevic 2000, PR-B Isoform-Selective Knockout Mouse (Science) Mouse knockout study — Lifespan Separated function of PR-A and PR-B isoforms, PR-A required for uterine and ovarian function; PR-B required for mammary alveologenesis 37
Conneely 2001, Lessons from Progesterone Receptor Isoform Knockout Mice Review — Synthesis Consolidated the isoform-selective biology of PR-A and PR-B and its implications for reproductive and breast physiology 38
Stanczyk 2013, Progestogens Used in Postmenopausal HT Review — Synthesis Standard reference for the pharmacology of progestogen heterogeneity, receptor binding, metabolite spectrum, intracellular actions, and clinical effects across bioidentical progesterone, MPA, norethindrone, levonorgestrel, drospirenone, and others 39
Schindler 2003, Classification and Pharmacology of Progestins Review — Synthesis Standard reference framework for classifying progestogens by chemical class (progesterone-derived, 17-OH-progesterone-derived, 19-nortestosterone-derived) and clinical receptor profile 40
Campagnoli 2005, Progestins and Progesterone in HRT and Breast Cancer Risk Review — Synthesis Argues, on the basis of E3N and mechanistic data, that synthetic progestins drive most of the breast-cancer signal in combined HRT and that bioidentical progesterone may be a lower-risk choice 41
Schumacher 2014, Progesterone and Allopregnanolone in the Nervous System (Prog Neurobiol) Review — Synthesis Standard reference for the neurosteroid biology of progesterone and allopregnanolone, GABA-A modulation, myelination, neuroprotection, mood, sleep, and seizure threshold 35
Guennoun 2015, Progesterone and Allopregnanolone CNS Response to Injury Review — Synthesis Mechanistic synthesis of progesterone/allopregnanolone neuroprotection literature; updated through the era of failed clinical TBI trials 36
Hargrove 1989, Absorption of Oral Progesterone Influenced by Vehicle and Particle Size Pharmacokinetic study in healthy women — Per-dose Micronization plus oil vehicle substantially improves oral progesterone absorption, pharmaceutical basis for Prometrium 13
De Ziegler & Bulletti 1997, The First Uterine Pass Effect Review of pharmacokinetic and tissue-distribution data — Synthesis Vaginal progesterone preferentially concentrates in the uterus relative to serum, the pharmacokinetic basis for vaginal route's efficacy in luteal support and short-cervix prophylaxis 15
Cicinelli 1998, Higher Uterine-Artery Than Radial-Artery Progesterone After Vaginal Administration Pharmacokinetic study in oophorectomized women — Per-dose Direct demonstration of preferential uterine vascular delivery of vaginal progesterone, confirmatory mechanism for the first uterine pass effect 16
NASEM 2020, Compounded Bioidentical Hormone Therapy Report Consensus committee report — Synthesis Acknowledged the legitimate role of compounded BHRT for documented patient-specific need; explicitly criticized routine substitution of compounded for FDA-approved products without clinical rationale and the use of transdermal progesterone creams for endometrial protection 12
NAMS 2022 Hormone Therapy Position Statement Society position statement — Synthesis Current consensus framework for menopausal HT including selection of progestogen for endometrial protection; references micronized progesterone as a reasonable choice with the caveat that head-to-head randomized data vs synthetic progestins are limited 11
Endocrine Society 2015 Treatment of Symptoms of the Menopause (Stuenkel) Clinical practice guideline — Synthesis Diagnostic and therapeutic framework for menopausal HT including discussion of progestogen choice 10

Mechanism detail

Detailed Mechanism of Progesterone

Progesterone receptor isoform biology. The PR gene is transcribed from two estrogen-induced promoters yielding PR-B (the full-length isoform, ~114 kDa) and the N-terminally truncated PR-A (~94 kDa). Both isoforms bind progesterone and the same DNA progesterone-response elements, but their N-terminal domains recruit different coregulators and produce different transcriptional outputs. PR-A can function as a transdominant repressor of PR-B in some tissue contexts. Isoform-selective knockout mice 37 38 demonstrated that PR-A is required for the antiproliferative endometrial effect of progesterone and for normal ovulation and decidualization, while PR-B is required for normal mammary gland alveologenesis during pregnancy and lactation. This isoform separation underlies why the tissue-specific effects of progesterone in uterus, breast, and brain are not interchangeable.

Neurosteroid pathway. Approximately 5, 15% of administered progesterone is metabolized by 5α-reductase to 5α-dihydroprogesterone and then by 3α-hydroxysteroid dehydrogenase to 5α-pregnan-3α-ol-20-one (allopregnanolone). Allopregnanolone is one of the most potent endogenous positive allosteric modulators of the GABA-A receptor, comparable in efficacy to benzodiazepines at synaptic GABA-A subtypes and uniquely active at tonic-inhibition extrasynaptic δ-subunit-containing GABA-A receptors 35 36. This pathway explains progesterone's CNS effects (sedation, anxiolysis, anticonvulsant action) and is the basis for the dose-dependent somnolence experienced with bedtime oral progesterone. The pathway is also why bedtime dosing of Prometrium is recommended and why bioidentical progesterone has CNS effects that synthetic progestins do not reproduce.

First uterine pass effect. Vaginally administered progesterone produces serum levels lower than oral or IM administration at comparable doses but concentrates in the uterus at concentrations several-fold higher than serum 15. Cicinelli demonstrated higher progesterone concentrations in uterine artery than in radial artery after vaginal administration, providing direct evidence of preferential uterine delivery 16. This pharmacokinetic feature is the basis for the efficacy of vaginal progesterone in luteal support and in preventing preterm birth in women with a short cervix, where local rather than systemic concentration is the relevant target 21 23.

Endometrial physiology. In estrogen-primed endometrium, progesterone via PR-A induces secretory transformation: glandular convolution, glycogen accumulation, stromal pre-decidualization, and ultimately decidualization if implantation occurs or menstrual sloughing if not. Pharmacologically, this antiproliferative effect on estrogen-driven mitosis is the mechanism by which adequate progestogen exposure prevents endometrial hyperplasia and adenocarcinoma in women receiving estrogen replacement. PEPI 1 established the quantitative threshold: estrogen-only therapy produced complex/atypical hyperplasia in ~10, 34% of cycles per arm, while estrogen plus micronized progesterone 200 mg cyclic 12 days/month produced rates indistinguishable from placebo. PEPI is the principal randomized evidence for oral micronized progesterone as endometrial-protective.

Pregnancy maintenance. Progesterone maintains uterine quiescence by reducing myometrial contractility (membrane progesterone receptor signaling), suppresses maternal cell-mediated immunity at the maternal-fetal interface, and supports decidual stability. In assisted reproduction, exogenous progesterone substitutes for the corpus luteum (which is suppressed in stimulated cycles) until the placenta becomes the dominant source. Vaginal and IM progesterone are the principal routes used in ART 17.

Breast tissue. Progesterone effects on normal and neoplastic breast tissue are complex and clinically consequential. The E3N cohort 6 reported that combined HRT with synthetic progestins (most commonly MPA in the European prescribing context) carried a higher breast-cancer risk than estrogen alone or estrogen plus bioidentical progesterone. The mechanistic interpretation, that progesterone's PR-A/PR-B isoform balance and lack of off-target androgen-receptor activity distinguish it from synthetic progestins on breast tissue, is supported by Campagnoli's reviews 41 and the Stanczyk progestogens framework 39. The randomized evidence for breast safety of bioidentical progesterone vs synthetic progestins in combined HRT remains observational; WHI 2 used MPA, not micronized progesterone.

CNS effects beyond GABA-A. Progesterone has progesterone-receptor and neurosteroid-mediated effects on sleep architecture (REM modulation), thermoregulation (the hypothalamic warming effect responsible for the luteal-phase basal temperature rise; also relevant to vasomotor symptoms in perimenopause), and seizure threshold (allopregnanolone's anticonvulsant effect underlies the catamenial-epilepsy biology characterized by Herzog 31 32).

Pharmacology

Progesterone Pharmacokinetics & Pharmacodynamics

Pharmacokinetics

Unmodified oral progesterone has very low bioavailability because of extensive first-pass hepatic metabolism 14. Micronization plus an oil vehicle (Prometrium uses peanut oil; compounded preparations can use olive, MCT, or other oils) substantially improves oral absorption 13. After oral micronized progesterone, serum levels peak at 1, 4 hours and decline over 8, 12 hours; substantial 5α-reduction to allopregnanolone in the gut wall and liver produces the characteristic somnolence within 1, 2 hours of oral dosing.

Vaginal progesterone produces lower peak serum levels than oral or IM at comparable mg dose but concentrates in the uterus via the first uterine pass effect 15 14. Cicinelli demonstrated that progesterone concentrations are higher in the uterine artery than in the radial artery after vaginal administration 16, direct evidence of preferential uterine vascular delivery. This makes the vaginal route ideal when uterine action (luteal support, short-cervix prophylaxis) is the goal.

IM progesterone in oil produces high stable serum levels and is the historical standard for ART luteal support in protocols where vaginal route is contraindicated or inadequate 14. Half-life of IM progesterone is approximately 7 hours but the depot release from oil extends pharmacodynamic effect to 24 hours or more.

Transdermal cream produces low and variable serum levels, orders of magnitude lower than oral or vaginal at typical compounded strengths, which is the pharmacokinetic basis for the position that creams are inadequate for endometrial protection 12 10 14.

Pharmacodynamics

Pharmacodynamic effects are tissue-specific and route-dependent 39. Endometrial action requires adequate serum or local concentration to produce secretory transformation, achieved at 100, 200 mg oral or 90, 200 mg vaginal daily in combined HRT 1. CNS effects (somnolence, anxiolysis, anticonvulsant) are dose-dependent and mediated by 5α-reduced metabolite allopregnanolone, concentrated in the first hours after oral dosing 35 36.

Breast tissue: PR-A/PR-B isoform-selective signaling 37 38 underlies the tissue-specific effects on breast that are functionally distinct from synthetic progestins. The observational evidence 6 supports the interpretation that bioidentical progesterone has a more favorable breast safety signal than MPA and other synthetic progestins in combined HRT, though randomized head-to-head data do not exist 39.

Comparative formulations

Comparing Progesterone Formulations

Choice of formulation balances indication, prior tolerability, and patient preference. For endometrial protection in combined HRT, oral Prometrium (or compounded oral capsule) at 100 mg continuous or 200 mg cyclic is the standard. For ART luteal support, vaginal gel (Crinone) or insert (Endometrin) is most common in US practice; IM progesterone in oil is an alternative for protocols with contraindication or inadequate response to vaginal 17. For short-cervix preterm-birth prophylaxis, vaginal compounded suppository 200 mg/day or vaginal gel is supported by the EPPPIC IPD meta-analysis 24. For perimenopausal vasomotor symptoms and sleep, oral micronized progesterone at bedtime 28 30 is the route used in the randomized literature.

Compounded preparations expand the route palette: troches and alternative-oil oral capsules address peanut-oil sensitivity to Prometrium; intermediate-strength oral capsules (50, 75, 150 mg) address titration needs; compounded vaginal suppositories address strengths not provided by Crinone or Endometrin 48. Transdermal cream is not appropriate as the progestogen arm of combined HRT for endometrial protection 12.

RonanRx compounds these preparations on patient-specific prescription 48. The pharmacist review confirms the prescribed formulation is responsive to a documented patient-specific need and is not routine substitution for a manufactured product.

Storage

Progesterone Storage and Handling

Compounded oral progesterone capsules in oil are stored at controlled room temperature (USP definition 20, 25°C, with allowed excursions 15, 30°C) protected from light. Vaginal suppositories and troches may require refrigeration depending on the base used (e.g., cocoa-butter suppositories soften at room temperature in warm climates and are typically refrigerated). Compounded creams are stored per the dispensing label.

Beyond-use dating follows USP <795> for non-sterile compounded preparations and USP <797> for sterile preparations (e.g., compounded IM progesterone if dispensed) 5049.

RonanRx operations

Progesterone Compounding & Operations

503A compounding

RonanRx compounds bioidentical progesterone preparations under 503A on patient-specific prescriptions. Non-sterile preparations (oral capsules, troches, vaginal/rectal suppositories, creams) follow USP General Chapter <795>. Sterile preparations (compounded IM progesterone, if dispensed) follow USP General Chapter <797> with documented active-ingredient sourcing (USP/NF grade), sterility and endotoxin testing per applicable risk-level requirements, gravimetric/volumetric verification, and full lot traceability 495012.

Progesterone is not a controlled substance. Standard prescription handling applies. Each prescription is verified for prescriber registration and patient identity before dispensing 47.

Pharmacist review

Each prescription for compounded progesterone undergoes pharmacist review prior to dispensing. The review confirms: a documented patient-specific clinical reason for the compounded preparation (peanut-oil sensitivity to Prometrium; need for a strength not provided manufactured; need for a route not provided manufactured; documented excipient sensitivity); appropriate indication framework (combined HRT endometrial protection, luteal support, short-cervix prophylaxis, catamenial epilepsy specialty management, or other documented clinical context); absence of contraindications 48.

Critical pharmacist-review boundary: RonanRx does not fill prescriptions for transdermal progesterone cream when the prescription documents endometrial-protection intent in a woman on systemic estrogen with an intact uterus. The serum levels produced by cream are inadequate for that purpose 12 10. In such cases the pharmacist contacts the prescriber to discuss an oral or vaginal alternative 11.

Quality and traceability

Progesterone API is sourced from FDA-registered facilities with documented certificates of analysis. Each batch is recorded with lot numbers traceable to API source, compounding date, beyond-use date, and dispensing pharmacist of record. Sterile preparations carry sterility and endotoxin test documentation per USP <797> risk-level requirements 5049.

Cold chain

Most compounded progesterone preparations are not cold-chain products. Oral capsules and creams ship at controlled room temperature. Cocoa-butter-based vaginal suppositories may require refrigerated shipping in warm seasons or climates; shipping instructions are determined per preparation. Patients are instructed to follow the dispensing-label storage instructions and to contact the pharmacy if shipping temperature integrity is in doubt.

FAQ

Frequently Asked Questions About Progesterone

Is compounded progesterone the same as Prometrium?

No. Prometrium is an FDA-approved manufactured product (oral micronized progesterone in peanut oil at 100 mg or 200 mg). Compounded preparations are pharmacy-prepared on patient-specific prescription and are not FDA-approved 4812. They are dispensed when a documented patient-specific clinical need is not met by Prometrium or another manufactured product, for example, peanut-oil sensitivity (requiring an alternative oil vehicle), a strength between 100 and 200 mg (such as 50, 75, or 150 mg), a troche or vaginal suppository at a strength the manufactured market does not provide, or a documented excipient sensitivity 47.

Why does my doctor want me to take progesterone at bedtime?

Oral micronized progesterone is converted in the gut and liver to allopregnanolone, a metabolite that activates the GABA-A receptor in the brain (the same receptor system that benzodiazepines and alcohol act on) 35. This produces predictable somnolence and mild dizziness within 1, 2 hours of dosing, which is a side effect during the day but a therapeutic effect at bedtime. Caufriez 2011 showed that bedtime oral progesterone improves sleep architecture in postmenopausal women, and this is the standard recommendation in combined HRT 30.

Is bioidentical progesterone safer than the progestins in WHI?

Maybe. The WHI used medroxyprogesterone acetate (MPA), not bioidentical progesterone 39. The E3N observational cohort suggested that combined HRT with bioidentical progesterone carries a smaller breast-cancer signal than combined HRT with synthetic progestins 6. NAMS and the Endocrine Society reference this when discussing progestogen choice 1110. But there is no head-to-head randomized trial of bioidentical progesterone vs MPA for combined-HRT safety endpoints, so the bioidentical advantage is observational rather than randomized 2.

Why is RonanRx unwilling to dispense progesterone cream for combined HRT?

Progesterone creams produce serum levels that are inadequate to reliably oppose estrogen-induced endometrial proliferation. Using a cream as the progestogen arm of combined estrogen HRT in a woman with an intact uterus puts her at risk of endometrial hyperplasia and adenocarcinoma. The NASEM 2020 report, NAMS 2022, and the Endocrine Society 2015 guideline all flag this 121110. Oral micronized progesterone or vaginal progesterone are the appropriate routes for endometrial protection.

Will progesterone help with my hot flashes?

The Hitchcock 2012 placebo-controlled trial and the Prior 2023 phase 3 Canada-wide trial show modest reduction in vasomotor symptoms with oral micronized progesterone 300 mg at bedtime 2829. NAMS 2022 does not list progesterone monotherapy as a first-line vasomotor-symptom therapy but acknowledges the evidence 11. For women who cannot or prefer not to take estrogen, oral micronized progesterone is one of several options worth discussing with the prescriber.

Why did Makena (17-OHPC) get withdrawn?

Makena was 17-α-hydroxyprogesterone caproate, a synthetic progestin, not bioidentical progesterone. The Meis 2003 trial showed reduction in recurrent preterm birth, leading to FDA accelerated approval 192524. The PROLONG 2020 confirmatory trial failed to replicate that benefit. FDA initiated withdrawal in 2023. Vaginal bioidentical progesterone for women with a sonographic short cervix retains evidence and remains in use, that's a different molecule and a different indication.

Does progesterone treat postpartum depression?

Oral progesterone has not been shown effective for postpartum depression in randomized trials 34. The validated mechanism is intravenous allopregnanolone (brexanolone, Zulresso, FDA-approved 2019), which is the GABA-A-modulating 5α-reduced metabolite of progesterone 35. This is the strongest clinical proof that the neurosteroid pathway distinguishes bioidentical progesterone from synthetic progestins, but it does not support oral progesterone as a treatment for postpartum depression.

Does RonanRx sell progesterone directly to patients?

No. Compounded progesterone is dispensed only on a patient-specific prescription written by a licensed prescriber for an identified patient, with pharmacist review before dispensing. RonanRx is not a direct-to-consumer storefront 47.

Clinician resource

Download the Progesterone Clinical Monograph (PDF)

The full white paper covers every section on this page plus chemical identity, evidence grading, indication-by-indication summaries, research gaps, and reference appendix. Suitable for sharing with prescribing doctors and pharmacist reviewers.

Download information packet ↓

References

References

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How to access

How to Access Progesterone

Compounded Progesterone is dispensed under 503A on a patient-specific prescription. Pick the path that matches where you're starting from.

For doctors

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A pharmacist will follow up within two business days. We'll cover state availability, supported formulations, and what integration looks like for your clinic.

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Patient with a doctor

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If your doctor has already prescribed Progesterone, sign up so we can prepare and ship your medication. The signup wizard collects intake and connects you to the prescribing workflow.

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Patient without a doctor

Find a partner clinic.

RonanRx prescribes through partner clinics — we don't initiate prescriptions on this site. See how the referral works and how to find a clinic in your state that has evaluated patients for Progesterone.

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