Norethisterone

How it works

It acts on progesterone receptors to oppose oestrogen-driven endometrial proliferation, stabilising the endometrium and, at higher exposure, suppressing the hypothalamic-pituitary-ovarian axis.

Prescribing in practice

• Although a progestogen, norethisterone is partly metabolised to ethinylestradiol, so it carries a venous thromboembolism risk and should be used with caution in women with thrombotic risk factors.
• It is contraindicated in undiagnosed vaginal bleeding and active venous thromboembolism, and bleeding may occur when treatment stops.
• It is not a reliable contraceptive at doses used for menstrual control and must not be relied upon for that purpose.

Monitoring

Assess bleeding pattern and symptom response, and review cardiovascular and thrombotic risk factors before and during use.

Counselling the patient

• This does not provide reliable contraception at the doses used for period control.
• A withdrawal bleed is expected a few days after stopping a short course to delay periods.
• Seek urgent advice for calf swelling or pain, chest pain or breathlessness.

Evidence & guidelines

Norethisterone is an established progestogen option in NICE guidance for heavy menstrual bleeding and related gynaecological indications.