Prometrium Regret, Stopping, and Restarting: What Real Patients and Clinical Data Actually Show

Side Effects in the Label's Trials

The most useful numbers are in the label's own adverse-reaction table, from a 3-year, placebo-controlled trial of postmenopausal women (178 on cyclic Prometrium plus conjugated estrogens vs 174 on placebo). Women taking cyclic Prometrium 200 mg plus conjugated estrogens 0.625 mg reported dizziness 15% vs 9% on placebo, depression 19% vs 12%, abdominal bloating 12% vs 5%, and breast tenderness 27% vs 6% [1]. Headache was 31% vs 27%, and joint pain was less common on active treatment, 20% vs 29% [1].

One detail changes how those figures should be read: the comparison is combination therapy against placebo pills containing no hormones, and every woman in the active arm also took estrogen, so the table cannot separate progesterone's contribution from estrogen's [1].

Sedation is the effect the label addresses directly. Prometrium "may cause transient dizziness and drowsiness and should be used with caution when driving a motor vehicle or operating machinery," and the label directs a single daily dose at bedtime [1]. During initial therapy a few women have experienced extreme dizziness or drowsiness, blurred vision, slurred speech, difficulty walking, loss of consciousness, vertigo, confusion, disorientation, feeling drunk, and shortness of breath [1][2].

Mood is murkier. The label's adverse-reaction table lists depression at 19% vs 12% [1], while the separate PEPI symptom analysis (875 women, conjugated estrogens with or without progestins) reported that anxiety, cognitive and affective symptoms did not differ by treatment assignment [5].

Boxed Warning and WHI Context

Prometrium has no boxed warning in its current label (Revision 02/2026). It was one of the first six menopausal hormone therapy products whose updated labeling FDA approved on 2026-02-12, with cardiovascular disease, breast cancer and probable dementia language removed from the boxed warning [3][4][2]. The WHI estrogen-plus-progestin data remain in the label's Warnings and Clinical Studies sections [2].

WHI tested conjugated estrogens 0.625 mg plus medroxyprogesterone acetate 2.5 mg in 16,608 women aged 50 to 79, and medroxyprogesterone is not micronized progesterone [1][6]. For that regimen the label reports invasive breast cancer relative risk 1.24 (95% CI 1.01 to 1.53), 9 more cases per 10,000 women-years (43 vs 35), with DVT relative risk 1.87, PE 1.98 and stroke 1.37 [1][6]. The French E3N cohort followed 80,377 postmenopausal women for a mean of 8.1 postmenopausal years and recorded 2,354 invasive breast cancers; compared with never-use, estrogen-progesterone combinations had a relative risk of 1.00 (95% CI 0.83 to 1.22), estrogen-dydrogesterone 1.16 (0.94 to 1.43), and estrogen with other progestagens 1.69 (1.50 to 1.91) [7]. E3N is an observational cohort, not a randomized trial.

What the Data Show About Endometrial Protection

For a postmenopausal woman with a uterus who takes estrogen, this is the part with real data. The label's endometrial trial randomized 358 women to Prometrium 200 mg for 12 days per 28-day cycle plus conjugated estrogens 0.625 mg (n=120), conjugated estrogens alone (n=119), or placebo (n=119), for up to 36 months. Endometrial hyperplasia was diagnosed in 6% of the combination group, 64% of the estrogen-alone group and 3% of the placebo group; atypical hyperplasia in 1%, 12% and 0% [1].

PEPI found the same pattern in 596 women with endometrial biopsies. On conjugated equine estrogen alone, simple hyperplasia occurred in 27.7% vs 0.8% on placebo, complex hyperplasia in 22.7% vs 0.8%, and atypical hyperplasia in 11.8% vs 0% [8]. All three estrogen-plus-progestin arms, including cyclic micronized progesterone 200 mg, had hyperplasia rates similar to placebo (P=.16) [8].

Two limits apply. These trials compared fixed regimens from the start rather than following women who stopped progesterone partway, and the estrogen studied was conjugated estrogens, not estradiol; the label does not describe use with estradiol [1].

What the Combination Does for Symptoms

Hot flashes and night sweats are where the combination does measurable work. In the label's trial, hot flashes were reported by 11% of women on Prometrium plus conjugated estrogens vs 35% on placebo, and night sweats by 7% vs 17% [1]. Across the PEPI cohort, every active treatment reduced vasomotor symptoms compared with placebo (odds ratios 0.17 to 0.28), with no additional benefit from adding a progestin to estrogen [5].

Micronized progesterone has also been tested alone for hot flashes. In a 12-week placebo-controlled trial, 133 healthy postmenopausal women with vasomotor symptoms took oral micronized progesterone 300 mg at bedtime (n=75) or placebo (n=58); symptom scores fell more on progesterone, with a mean adjusted difference of -4.3 (95% CI -6.6 to -1.9), and 8 women on progesterone and 4 on placebo stopped for adverse events [9]. That 300 mg bedtime dose is not one of the two regimens in the label [1].

Restarting: What the Label Specifies

The label sets out no restart schedule. What it does specify is narrow: 200 mg at bedtime for 12 days sequentially per 28-day cycle, alongside daily conjugated estrogens tablets, for a postmenopausal woman with a uterus; or 400 mg at bedtime for 10 days for secondary amenorrhea [1].

The label's contraindications are: hypersensitivity to the ingredients (the capsules contain peanut oil and are contraindicated in peanut allergy), abnormal genital bleeding of unknown cause, known or suspected or prior breast cancer, active or prior deep vein thrombosis or pulmonary embolism, active or prior arterial thromboembolic disease such as stroke or myocardial infarction, and known liver dysfunction or disease [1].

The label says Prometrium should be stopped immediately if a PE, DVT, stroke or MI occurs or is suspected. It also says that, when feasible, treatment should be stopped at least 4 to 6 weeks before surgery of the type associated with an increased risk of thromboembolism, or during periods of prolonged immobilization, and that Prometrium should be discontinued if a hormone-sensitive malignancy is diagnosed [2]. The label says progesterone may cause some degree of fluid retention, and that women with cardiac or renal dysfunction warrant careful observation [1]. It says the capsules should not be used during pregnancy, and that detectable progestin has been found in the milk of nursing women and caution is advised [2].

Compounded Progesterone Is Not FDA-Approved

The label describes Prometrium as micronized progesterone "chemically identical to progesterone of human ovarian origin," made from a plant-source starting material, with oral bioavailability increased by micronization [2]. Compounded progesterone is not FDA-approved, and FDA does not verify the safety, effectiveness or quality of compounded drugs before they are marketed [10].