Norethindrone
Norethindrone (norethisterone outside US)
Aygestin (5 mg, Rx); Camila, Errin, Heather, Jolivette, Nor-QD, Ortho Micronor, Sharobel (0.35 mg POPs); component of many COCs
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Summary
Common uses
Progestin-only oral contraception0, Secondary amenorrhea0, Endometriosis0, Dysfunctional uterine bleeding0, Endometrial protection in estrogen-containing HRT0
Pharmacy
Starting dose
POP: 0.35 mg PO daily continuously (no placebo week); high-dose 5 mg Aygestin for amenorrhea/endometriosis 5-10 mg/d
Preparations
0.35 mg POP tablets; 5 mg tablets (Aygestin); component of COCs and combination HRT
US FDA Max
Indication-specific
Pharmacology
Routes
Oral
Onset
Contraception within 48 hours of starting (POP); endometrial effects days
Duration
~24 hours per dose (strict timing required for POP — within 3-hour window each day)
Half-life
~8 hours[1]
Bioavailability
~65% (oral)[1]
Pregnancy
Contraindicated in known pregnancy (Aygestin); the 0.35 mg POP is not teratogenic and does not need to be discontinued before conception planning.[citation needed]
Legal status
Rx-only in US (note: norgestrel 0.075 mg POP is now OTC as Opill since 2023, but norethindrone POP remains Rx)
Purported mechanism
Norethindrone is a 19-nortestosterone-derived progestin with progesterone receptor agonism plus weak androgen and estrogen receptor activity; the contraceptive effect comes primarily from cervical mucus thickening (the dominant POP mechanism at 0.35 mg, since ovulation suppression is incomplete) plus endometrial decidualization.0 Higher-dose Aygestin (5 mg) achieves more reliable ovulation suppression and is used for endometriosis and DUB. POP requires strict daily timing because the 24-hour cervical-mucus effect window is narrower than COC[1].
References
- ↑ 1.0 1.1 1.2 FDA Prescribing Information, Ortho Micronor (norethindrone), Janssen, current revision. https://www.accessdata.fda.gov/drugsatfda_docs/label/2008/017558s066lbl.pdf