A Guide to Norethisterone: Dosage, Side Effects and How to Buy in the UK

Norethisterone is the UK’s most widely prescribed period delay medication — a synthetic progestogen used to safely postpone menstruation for holidays, weddings, sporting events, or any personal reason. Taken as one 5mg tablet three times daily, starting at least 3 days before your expected period, norethisterone delays your period for as long as you continue the course. This comprehensive guide covers how norethisterone works, dosage, side effects, contraindications, and all your alternatives.

Key Facts at a Glance

How Norethisterone Works

During the normal menstrual cycle, progesterone levels drop at the end of the luteal phase, signalling the uterine lining to shed. Norethisterone mimics progesterone, keeping these levels artificially elevated and maintaining the uterine lining — postponing menstruation. Once tablets are stopped, progesterone levels fall and the period begins within 2–4 days.

Additional effects include thickening of cervical mucus and, with prolonged use at therapeutic doses for endometriosis, suppression of endometrial growth and mild anti-oestrogenic activity.

How Effective Is Norethisterone?

When taken correctly, norethisterone is highly effective at delaying menstruation. Clinical evidence shows it successfully postpones periods in the vast majority of women who follow the regimen. Approximately 1 in 10 women may experience light spotting or breakthrough bleeding — this does not mean the medication has failed and is not a reason to stop.

Side Effects

• Acne or skin changes
• Low mood or mood changes
• Fluid retention and bloating
• Breast tenderness
• Reduced libido
• Nausea or headaches

Who Should Not Take Norethisterone?

• Pregnant or may be pregnant
• Breastfeeding
• Personal history of blood clots (DVT, PE)
• Severe liver disease
• Hormone-sensitive cancers
• Unexplained vaginal bleeding

Drug Interactions

• Epilepsy medications (phenytoin, carbamazepine)
• HIV antivirals (ritonavir, nelfinavir)
• Tuberculosis antibiotics (rifampicin, rifabutin)
• Warfarin (anticoagulant)
• St John’s Wort herbal supplement
• Certain antibiotics (tetracyclines)

Alternatives to Norethisterone for Period Delay

• Combined oral contraceptive pill — taking active pills continuously skips withdrawal bleeds; also provides contraception
• Progesterone-only pill (mini pill) — taken continuously, can significantly reduce or stop periods
• Hormonal IUD (Mirena) — releases steady low-dose progestogen; often reduces or stops periods long-term
• Depo-Provera injection — 12-weekly contraceptive injection that often suppresses menstruation

For more information about period delay and when it is appropriate, see our guides on Period Delay Facts and Can You Delay Your Period?