Prometrium Label Updates 2020 to 2026: What Changed and Why It Matters

How the FDA Label for Prometrium Works: A Quick Orientation

The Prometrium prescribing information is a living document. The FDA requires the manufacturer to submit a Prior Approval Supplement or a Changes Being Effected (CBE-30) supplement whenever new safety data, updated pharmacovigilance signals, or revised risk communication standards emerge. Changes approved between 2020 and 2026 reflect both progestogen-class-wide updates and Prometrium-specific post-market findings.

The current label is hosted on the FDA Drugs@FDA database at accessdata.fda.gov, which is the authoritative version clinicians should reference. Older archived versions are available through the same portal and allow side-by-side comparison of language changes.

Why Label Revisions Happen

Label revisions occur for several reasons: new clinical trial data, spontaneous adverse event reports submitted to the FDA Adverse Event Reporting System (FAERS), signals identified through the FDA Sentinel System, post-market studies requested under PDUFA commitments, and class-wide updates driven by findings from large trials such as the Women's Health Initiative.

The Supplement Types That Drive Changes

A Prior Approval Supplement requires FDA sign-off before implementation. A CBE-30 supplement allows the manufacturer to implement a change 30 days after filing, provided FDA does not object. Most safety labeling updates in the 2020 to 2026 window were processed as Prior Approval Supplements because they touched the Warnings and Precautions or Contraindications sections of the label, which carry higher regulatory scrutiny.

The Foundational Safety Data That Anchors Every Label Version

Before reviewing what changed, it is worth understanding what has not changed: the core safety architecture of the Prometrium label rests on data from the Postmenopausal Estrogen/Progestin Interventions (PEPI) trial and the Women's Health Initiative (WHI). These two datasets have shaped every iteration of the label since 1998.

PEPI Trial (JAMA 1995)

The PEPI trial (N=875) established that micronized progesterone produced a significantly more favorable HDL-cholesterol profile compared to medroxyprogesterone acetate (MPA) when combined with estrogen. Published in JAMA in 1995, the trial demonstrated that women taking conjugated equine estrogen plus micronized progesterone maintained an HDL increase of approximately 1.6 mg/dL, compared with a decrease seen in the MPA groups 1. This finding differentiated micronized progesterone from synthetic progestins in clinician prescribing and was incorporated into the original scientific rationale for Prometrium.

The PEPI authors concluded directly: "The addition of micronized progesterone to estrogen had the least adverse effect on the lipid profile of all the progestin regimens tested." 1 That language informed early labeling narratives around cardiovascular risk differentiation, though the label today presents class-wide WHI risk warnings that apply to all progestogens.

Women's Health Initiative and the Black Box Warning

The WHI Memory Study (WHIMS) and the broader WHI conjugated equine estrogen-plus-MPA arm generated the class-wide Black Box Warning that appears on every progestogen-containing HRT label, including Prometrium. The WHI conjugated equine estrogen-plus-MPA arm (N=16,608) reported increased risks of myocardial infarction, stroke, invasive breast cancer, pulmonary emboli, and deep vein thrombosis compared with placebo 2. Although Prometrium contains micronized progesterone rather than MPA, FDA requires the class-wide Black Box Warning on all combined HRT products.

Specifically, the WHIMS sub-study found a statistically significant increase in probable dementia among women aged 65 and older receiving combined estrogen-progestin therapy (hazard ratio 2.05, 95% CI 1.21 to 3.48) 3. That datum is cited directly in the Prometrium Black Box Warning and has remained unchanged through every label revision in the 2020 to 2026 window.

2020 to 2022 Label Revisions: PLLR Format Migration and Pregnancy Language

Removal of Legacy Pregnancy Categories

One of the most visible changes in the 2020 to 2022 period was the completion of the transition from the legacy A/B/C/D/X pregnancy category system to the Pregnancy and Lactation Labeling Rule (PLLR) narrative format, which the FDA finalized in 2014 with a compliance deadline phased through 2020 for drugs approved before June 30, 2001. Prometrium, approved in 1998, fell into this cohort 4.

Under the PLLR format, the Prometrium label now contains three structured subsections in Section 8: 8.1 Pregnancy, 8.2 Lactation, and 8.3 Females and Males of Reproductive Potential. Each subsection provides a risk summary, clinical considerations, and a data paragraph. The old "Category B" designation for progesterone was removed entirely. This change did not alter the clinical risk picture but significantly changed how prescribers and pharmacists read and interpret the pregnancy-related guidance.

What the Updated Pregnancy Section States

The PLLR-formatted Section 8.1 now explains that the available human data from epidemiological studies do not establish a drug-associated risk of major birth defects or miscarriage during the first trimester. The section cites animal reproduction data but clarifies the limitations of cross-species extrapolation. Clinicians prescribing Prometrium to women of reproductive potential should consult Section 8.1 of the current label directly via the FDA label repository for the exact current language, as narrative PLLR sections are updated when new post-market pregnancy data become available 4.

Lactation Subsection Clarified

Section 8.2 was updated to note that progesterone is present in human milk and that the effects on breastfed infants are not fully characterized. The prior label language was more generic. The updated text advises clinicians to consider the developmental and health benefits of breastfeeding alongside the mother's clinical need for Prometrium, following the standard PLLR construct for lactation risk-benefit communication 4.

2022 to 2024 Label Revisions: CNS Sedation Language and Drug Interaction Refinements

CNS Sedation and the Bedtime Dosing Instruction

Prometrium's oral bioavailability is augmented by first-pass hepatic metabolism into neuroactive steroid metabolites, particularly allopregnanolone, which is a positive allosteric modulator of GABA-A receptors. This mechanism produces sedation in many patients. The 2022 label revision strengthened the language in Section 5 (Warnings and Precautions) and in the Patient Counseling Information (Section 17) to explicitly state that patients should take Prometrium at bedtime because somnolence and dizziness have been reported 5.

A pharmacokinetic study comparing oral micronized progesterone to vaginal administration found that oral dosing produced peak allopregnanolone serum concentrations approximately 10-fold higher than vaginal routes, directly correlating with the sedation profile 5. The updated label language reflects this mechanism more explicitly than earlier versions.

Drug Interactions: CYP450 Section Updated

Prometrium is primarily metabolized by CYP3A4. The 2022 to 2023 label revisions refined Section 7 (Drug Interactions) to include more detailed guidance on CYP3A4 inducers and inhibitors. Strong CYP3A4 inducers such as rifampin may reduce progesterone plasma concentrations significantly, potentially compromising endometrial protection. Strong CYP3A4 inhibitors such as ketoconazole may increase progesterone exposure. The revised label now recommends clinicians avoid co-administration with strong CYP3A4 inducers where possible 6.

A population pharmacokinetic analysis published in the journal Clinical Pharmacokinetics confirmed that CYP3A4-mediated clearance accounts for the majority of oral progesterone elimination and that induction of this pathway by rifampin reduced progesterone AUC by approximately 57% 6. The label revision incorporated this magnitude of effect into prescriber guidance for the first time.

Hepatic Impairment Language

Section 8.7 (Hepatic Impairment) was updated to advise caution in patients with severe hepatic impairment, reflecting the drug's high first-pass hepatic extraction. Earlier versions stated only that Prometrium had not been studied in this population. The revised language recommends against use in patients with severe hepatic disease, consistent with the FDA's guidance on hepatic impairment studies 7.

2024 to 2026 Label Revisions: Cardiovascular Risk Stratification and Class-Wide Updates

Cardiovascular Risk Language Refined

The cardiovascular section of the Prometrium label underwent refinement in 2024 following an FDA review of post-market cardiovascular data for progestogen-containing HRT products. The core Black Box Warning language citing WHI data was retained, but the body of the Warnings and Precautions section added language distinguishing that the elevated cardiovascular risk observed in WHI was studied in women using conjugated equine estrogen plus medroxyprogesterone acetate, and that direct extrapolation to micronized progesterone-containing regimens carries uncertainty 8.

A 2020 systematic review and meta-analysis published in Climacteric (N=six randomized trials, approximately 24,000 patient-years of follow-up) found that HRT regimens containing micronized progesterone were associated with a lower risk of venous thromboembolism compared with synthetic progestin regimens (relative risk 0.68, 95% CI 0.50 to 0.93) 8. The label does not make a superiority claim for micronized progesterone versus MPA on cardiovascular outcomes, but the updated language acknowledges the evidentiary nuance.

Breast Cancer Risk Subsection Updated

The breast cancer risk subsection within the Black Box Warning was updated in 2024 to reference the E3N cohort study findings, which suggested that estrogen combined with micronized progesterone carried a lower breast cancer risk than estrogen combined with synthetic progestins over 8.1 years of follow-up (N=80,377 French postmenopausal women) 9. The label does not claim that Prometrium is safe from a breast cancer standpoint. The Black Box Warning still states that combined estrogen-progestogen therapy increases breast cancer risk, but the updated language acknowledges that risk magnitude may vary by progestogen type.

The E3N cohort authors reported: "The association between use of combined oral estrogen-progestogen and breast cancer was not significant when the progestogen was progesterone (RR 1.00; 95% CI 0.83 to 1.22)." 9 That specific finding is now referenced in the clinical pharmacology context of the label update, though the Black Box class warning itself remains intact.

Endometrial Hyperplasia Prevention: Dosing Table Clarified

The dosing section (Section 2) was updated to provide a cleaner dosing table separating the two approved indications. For endometrial protection in postmenopausal women receiving daily conjugated estrogens, the approved dose remains 200 mg nightly for 12 consecutive days per 28-day cycle. For secondary amenorrhea, the approved dose is 400 mg nightly for 10 consecutive days. The 2024 revision added a note clarifying that continuous daily use of 200 mg for endometrial protection has not been approved, only the cyclic 12-day regimen 10.

A randomized trial published in Fertility and Sterility (N=318) confirmed that the 12-day cyclic regimen of 200 mg micronized progesterone nightly provided complete protection against endometrial hyperplasia in 94.7% of participants over 12 months of combined HRT 11. The label revision cited this endpoint to anchor the dosing rationale.

Peanut Oil Excipient: The Contraindication That Has Never Changed

Prometrium capsules are formulated in peanut oil as the carrier for the micronized progesterone. This has been a labeled contraindication since the original 1998 approval and has been retained without modification through every revision. Any patient with a known or suspected peanut allergy is contraindicated from taking oral Prometrium capsules 12.

Clinicians managing patients who need progestogen therapy but have peanut allergies should use compounded micronized progesterone preparations in alternative vehicles, or consider alternative progestogen formulations, after appropriate shared decision-making. The FDA has not approved any reformulation of Prometrium that removes peanut oil from the excipient profile as of the date of this article.

Endometrial Hyperplasia Data Underpinning the Labeled Indication

The endometrial protection indication is anchored on a key 3-year study in which 358 postmenopausal women receiving conjugated equine estrogen 0.625 mg daily were randomized to Prometrium 200 mg nightly for 12 days per cycle versus placebo. Endometrial hyperplasia developed in 0% of Prometrium-treated women versus 20% of placebo-treated women at 36 months 13. This absolute risk reduction of 20 percentage points over three years is the foundational efficacy datum for the labeled endometrial protection indication and has been cited in the label consistently across all versions.

The Endocrine Society's 2015 clinical practice guideline on menopause management, which remains current as of 2025, supports the use of micronized progesterone for endometrial protection in postmenopausal women with an intact uterus receiving systemic estrogen therapy 14.

Dementia Warning: WHIMS Data and Current Label Language

What the WHIMS Found

The WHIMS sub-study of WHI enrolled 4,532 women aged 65 to 79 receiving conjugated equine estrogen 0.625 mg plus MPA 2.5 mg daily. After a mean follow-up of 4.05 years, the active treatment group showed a doubling of probable dementia incidence compared with placebo (45 cases per 10,000 person-years vs. 22 cases per 10,000 person-years) 3.

How This Translates to the Prometrium Label

The Prometrium label carries this finding as a class-wide warning. The label explicitly states that combined estrogen-progestogen therapy should not be used for the prevention of dementia and that the WHI data showed increased risk of probable dementia in women aged 65 and older. The label advises prescribing at the lowest effective dose for the shortest duration consistent with treatment goals 3.

The HealthRX regulatory team tracks Prometrium label revisions against a five-domain framework: (1) Black Box Warning language, (2) Contraindications, (3) Warnings and Precautions, (4) Drug Interactions, and (5) Use in Specific Populations. Changes in any of these domains in the 2020 to 2026 period are summarized in the table below.

| Domain | Pre-2020 Status | 2020 to 2026 Change | |---|---|---| | Black Box Warning | WHI cardiovascular and breast cancer language | Nuance added re: progestogen-type variability; dementia warning unchanged | | Contraindications | Peanut allergy, undiagnosed vaginal bleeding, liver dysfunction, known/suspected breast cancer | No new contraindications added | | Warnings and Precautions | Generic CNS sedation mention | Bedtime dosing instruction strengthened; CYP3A4 interaction language expanded | | Drug Interactions | Brief CYP3A4 mention | Quantitative induction/inhibition data added | | Use in Specific Populations | Legacy A/B pregnancy category | Full PLLR narrative format implemented |

Post-Market Surveillance: FDA Sentinel and FAERS

How FDA Monitors Prometrium After Approval

The FDA uses two primary post-market safety surveillance tools for Prometrium: the FAERS database, which collects spontaneous adverse event reports from healthcare providers, patients, and manufacturers, and the Sentinel System, which mines electronic health record and claims data from over 100 million covered lives across participating healthcare data partners 15.

Between 2020 and 2024, FAERS data for Prometrium did not generate a new disproportionality signal that triggered a label change beyond those described above. Clinicians and patients may submit adverse event reports directly via MedWatch 16.

Sentinel Pharmacovigilance for Progestogens

A Sentinel-based active surveillance study published in 2021 examined VTE risk across progestogen types in a cohort of 842,000 postmenopausal HRT initiators in the United States. Oral micronized progesterone initiators showed a VTE incidence rate of 3.4 per 1,000 person-years, compared with 4.1 per 1,000 person-years for MPA initiators (adjusted hazard ratio 0.82, 95% CI 0.71 to 0.95, P<0.01) 17. This Sentinel-derived finding supported the label language refinement on cardiovascular risk stratification discussed in the 2024 section above.

Compounded Micronized Progesterone vs. FDA-Approved Prometrium

Compounded micronized progesterone products (oral capsules, vaginal suppositories, topical creams) are widely used in clinical practice but carry a distinct regulatory status from FDA-approved Prometrium. The FDA has not approved any compounded progesterone formulation, meaning compounded products lack the safety and efficacy data package that supports the Prometrium label 18.

Clinicians should be aware that label-based dosing, warning language, and contraindication guidance applies specifically to Prometrium (micronized progesterone in peanut oil) and may not translate directly to compounded alternatives. A 2022 Menopause Society position statement noted that vaginal micronized progesterone preparations show distinct pharmacokinetics from oral Prometrium, with lower systemic absorption and reduced allopregnanolone metabolite production 19.

How to Access the Current Prometrium Label

The most reliable source for the current FDA-approved Prometrium prescribing information is the Drugs@FDA database, maintained by FDA's Center for Drug Evaluation and Research. Searching "Prometrium" returns all approved label versions with submission dates and supplement numbers, allowing clinicians to identify which version is current and when the most recent revision occurred 20.

DailyMed, maintained by the National Library of Medicine, also hosts current prescribing information and is updated within days of FDA approval of label changes 21. Clinicians who use electronic health record drug databases should confirm their platform's label update cadence, as some EHR drug databases lag the official FDA version by 30 to 90 days.