Detailed definition
Native progesterone is poorly absorbed orally because of rapid hepatic clearance. Micronization — reducing particle size to ~10 microns — improves bioavailability sufficiently to allow effective oral dosing. The active ingredient is bioidentical progesterone, identical in structure to that produced by the corpus luteum. Micronized progesterone is available as Prometrium and as generics in 100 mg and 200 mg capsules. Bedtime dosing is preferred because the allopregnanolone metabolite produces sedation, which is beneficial in menopause but might be disruptive if taken in the morning. Compared to synthetic progestins, observational data suggest a more favorable breast cancer profile (notably the French E3N study and meta-analyses showing reduced or absent breast cancer signal with micronized progesterone vs. medroxyprogesterone over 5+ years).
Why it matters in menopause
For women with a uterus on systemic estrogen, micronized progesterone is the modern preferred choice — both for the safety profile relative to medroxyprogesterone and for the sleep benefit. ClearedRx routinely pairs transdermal estradiol with bedtime oral micronized progesterone.
Related terms
Sources
External references: Wikipedia.