Norethisterone: Clinical Evidence & Trials
Norethisterone is a hormonal agent used for contraception, hormone replacement therapy, or the management of menstrual and gynecological disorders.
Hormonal contraceptives are among the most extensively studied medications with strong evidence for contraception, PCOS, endometriosis, and cancer prevention.
Evidence Strength
Level A (Strong) for contraception (>99% perfect-use efficacy), PCOS symptoms, endometriosis, and dysmenorrhoea.
Key Clinical Trial Findings
- •Pearl Index — combined OCP: 0.1–0.3 (perfect use); progestin-only pill: 0.3–1.0; depot medroxyprogesterone: 0.1–0.3
- •PCOS — Cochrane review: COC reduces androgen levels and acne in >80% of women; regulates cycles in 90%+
- •Endometriosis — ESHRE guidelines 2014/2022: COC reduces dysmenorrhoea NRS score by >4 points; continuous COC reduces lesion recurrence post-surgery
- •Ovarian cancer prevention — 10-year COC use reduces ovarian cancer risk by ~40% (Oxford FPA Study, Lancet 2008)
- •Endometrial cancer protection — >50% risk reduction with 5+ years of COC use
- •VTE risk — third/fourth-generation progestins carry 2–3× higher VTE risk vs levonorgestrel; absolute risk remains low (~3–9 per 10,000 women/year)
Numbers Needed to Treat (NNT)
Contraception (1 year): NNT ≈ 1 to prevent 1 unintended pregnancy vs no contraception (85% rate). Ovarian cancer (10 years): NNT ≈ 100 to prevent 1 ovarian cancer at average risk. Endometriosis dysmenorrhoea: NNT ≈ 3 for >50% pain reduction.
Guideline Recommendations
FSRH (UK), ACOG (US), WHO Medical Eligibility Criteria for Contraceptive Use. COC WHO Category 4 (contraindicated) in: migraine with aura, prior VTE, cardiovascular disease, smokers >35, breastfeeding <6 weeks. Drospirenone-containing pills preferred for PCOS (anti-androgenic effect).
Conditions Treated with Norethisterone
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