norethindrone
Brand: Micronor, Errin, Camila, Aygestin
Prototype: medroxyprogesterone
Drug Class: progestogen
Drug Family: hormone
Subclass: 19-nortestosterone progestogen — oral contraceptive and hormone therapy
Organ Systems: endocrinereproductive
Mechanism of Action
Progesterone receptor agonist that prevents pregnancy via thickening of cervical mucus, thinning of endometrium, and (at higher doses) inhibition of ovulation. Used as a progestin-only oral contraceptive ('mini-pill') and for management of endometriosis and abnormal uterine bleeding.
progesterone receptor
Indications
- contraception (progestin-only pill)
- endometriosis (Aygestin — norethindrone acetate)
- abnormal uterine bleeding
- secondary amenorrhea
Contraindications
- undiagnosed vaginal bleeding
- known or suspected pregnancy
- liver disease
- breast cancer
Adverse Effects
Common
- irregular menstrual bleeding
- amenorrhea
- headache
- breast tenderness
- nausea
Serious
- ectopic pregnancy (if contraceptive failure)
- VTE (lower risk than combination OCPs)
- depression
Pharmacokinetics (ADME)
| Absorption | oral; rapidly absorbed |
| Distribution | highly protein bound (SHBG, albumin) |
| Metabolism | hepatic; first-pass effect |
| Excretion | renal and fecal |
| Half-life | 5–14 hours |
| Onset | hours |
| Peak | 1–2 hours |
| Duration | 24 hours (requires consistent daily dosing within 3-hour window) |
| Protein Binding | 61% (albumin) + SHBG |
| Vd | 4 L/kg |
Drug Interactions
| Drug / Agent | Mechanism | Severity |
|---|---|---|
| CYP3A4 inducers | reduced norethindrone levels; potential contraceptive failure | major |
Nursing Considerations
- Must be taken at the SAME TIME every day within a 3-hour window to maintain contraceptive efficacy; missing by more than 3 hours requires 48 hours of backup contraception.
- Preferred oral contraceptive in breastfeeding women (no estrogen component means no reduction in milk supply).
- Appropriate for women who cannot take estrogen: migraines with aura, VTE history, hypertension, age >35 and smoking.
- Educate patients about irregular bleeding being common and expected; this does not indicate contraceptive failure.
Clinical Pearls
- The progestin-only pill ('mini-pill') requires more strict daily dosing adherence than combination OCPs due to its shorter half-life; a 3-hour window for taking the pill (vs. 12 hours for combination pills) must be clearly communicated.
- Norethindrone has moderate androgenic activity, which may contribute to acne in sensitive individuals — unlike desogestrel or norgestimate, which are preferred for patients with androgenic side effects.
Safety Profile
Pregnancy contraindicated
Lactation safe
Renal Adjustment Not required
Hepatic Adjustment Required
TDM Not required
Concordance Terms
Cross-referenced clinical concepts — click any term to see all content where it appears.