Progesterone is prescribed alongside estrogen in women with an intact uterus to prevent endometrial hyperplasia and cancer. Unopposed estrogen on an intact endometrium raises cancer risk substantially — pairing it with a progestogen reverses that risk.
Formulation choices
Oral micronized progesterone (bioidentical):
- Prometrium (US), Utrogestan (outside US)
- Taken at bedtime (common side effect: drowsiness, sometimes used for sleep benefit)
- Bioidentical — molecularly identical to human progesterone
Synthetic progestins:
- Medroxyprogesterone acetate (Provera) — the WHI study drug
- Norethindrone acetate — often in combination patches (CombiPatch) and oral formulations
- Levonorgestrel IUD (Mirena) — off-label for endometrial protection in HRT
Cyclic vs continuous dosing
- Continuous: Daily progesterone. Over time, produces no withdrawal bleed. Most common postmenopausal regimen.
- Cyclic: Progesterone 12-14 days per month. Produces a scheduled withdrawal bleed. More common perimenopausally.
When the IUD fits
A levonorgestrel IUD (Mirena) can provide endometrial protection for women on systemic estrogen without requiring them to take a separate oral progestogen. Off-label for this use but well-supported.