Norethisterone
A first-generation 19-nortestosterone-derived progestin, one of the earliest oral progestins. Used in contraceptives, HRT, menstrual delay and heavy bleeding. Retains mild androgenic activity and is partly converted to ethinylestradiol.
01 Overview
Norethisterone (norethindrone) is a widely used progestin dating to the 1950s. It appears in combined and progestin-only contraceptives, in HRT for endometrial protection, and is prescribed short-term to delay menstruation or manage heavy or painful periods.
As a 19-nortestosterone derivative it has mild androgenic and estrogenic activity; a small fraction is metabolised to ethinylestradiol at higher doses, which contributes a modest estrogenic and thrombotic effect. It is generally well tolerated but shares the class caveats around thrombosis.
02 Mechanism
Progesterone-receptor agonist with weak androgenic activity that thickens cervical mucus, thins endometrium and (at higher doses) suppresses ovulation; partially aromatised/metabolised to ethinylestradiol.
03 Dosing
| Tier | Dose | Route | Notes |
|---|---|---|---|
| Menstrual delay / bleeding | 5–15 mg/day | Oral | 5 mg two-three times daily; progestin-only pill uses 0.35 mg. |
04 Effects
| Effect | Magnitude | Evidence | |
|---|---|---|---|
| Menstrual controlDelays menstruation and reduces heavy menstrual bleeding. | Clinical | ||
| ContraceptionEffective in progestin-only and combined pills. | Clinical |
05 Side effects
| Effect | Severity | Frequency | Evidence | Countermeasures |
|---|---|---|---|---|
| Breakthrough bleedingIrregular spotting, especially early in use. | Mild | Common | Clinical | |
| Thromboembolic riskHigher-dose regimens carry VTE risk partly via EE conversion. | Severe | Rare at high dose | Clinical |