There is no established equivalent cream dosage for 100 mg oral progesterone
The evidence does not support a reliable dose conversion between oral micronized progesterone and topical progesterone cream because absorption is highly variable and unpredictable with transdermal formulations.
Why Direct Conversion Is Not Possible
The FDA-approved oral micronized progesterone demonstrates predictable, dose-proportional pharmacokinetics. At 100 mg daily, it produces a mean AUC of 43.3 ± 30.8 ng × hr/mL and Cmax of 17.3 ± 21.9 ng/mL 1. However, progesterone creams lack this pharmacokinetic consistency.
Evidence on Progesterone Cream Absorption
Research comparing OTC progesterone cream (40 mg twice daily = 80 mg total daily) to oral progesterone 200 mg showed similar systemic exposure (median AUC 12.5 vs 10.5 ng × h/mL) 2. This suggests approximately 80 mg of cream might approximate 200 mg oral, but this is problematic for several reasons:
- Absorption variability is extreme: Different application sites, skin conditions, and individual factors dramatically affect uptake
- Sub-therapeutic levels common: One study using 40 mg daily cream with transdermal estrogen produced only median progesterone levels of 2.5 nmol/L—well below luteal phase levels 3
- No FDA approval: Progesterone creams are not FDA-approved for systemic hormone therapy
Clinical Recommendation
Do not substitute progesterone cream for oral progesterone. The Endocrine Society explicitly recommends against custom-compounded hormones and advocates for FDA-approved preparations 4.
If oral progesterone is not tolerated:
- Consider vaginal micronized progesterone (FDA-approved, predictable absorption)
- Explore transdermal progesterone patches (if available and approved)
- Discuss alternative synthetic progestogens with established systemic bioavailability 4
Critical Pitfall
The study showing comparable exposure used 80 mg cream to match 200 mg oral 2—but even this cannot be extrapolated reliably. The authors themselves questioned whether topical progesterone should be available OTC given safety concerns with unmonitored systemic exposure.
For endometrial protection in women with a uterus taking estrogen, only FDA-approved progestogen formulations with proven efficacy should be used 4.