How period-delay tablets work — and what they do not do

People may want to delay a period for travel, sport, an exam or an important event. Norethisterone is a progestogen medicine that maintains hormone levels so the lining of the womb is not shed at the expected time. NHS medicines guidance says it normally needs to be started at least three days before the period is expected.

Bleeding usually returns after the medicine is stopped, although timing varies. If bleeding has already started, a period-delay course is unlikely to work as intended. Give the prescriber an honest estimate of your cycle dates and explain if your periods are irregular.

This is the most important distinction: norethisterone used for period delay does not prevent pregnancy. Use an appropriate contraceptive method if pregnancy is possible. If a period is late before treatment or pregnancy could already have occurred, take a pregnancy test and seek clinical advice.

People who already use a combined contraceptive pill may sometimes delay bleeding by taking active pills without a break, but the method depends on the pill. Ask a pharmacist, GP or sexual-health clinician rather than changing the schedule without advice.

A prescriber will consider your age, smoking, body-mass index, migraines, personal or family history of blood clots, liver disease, unexplained bleeding and medicines. These details change the balance of benefit and risk.

Seek medical advice for unusually heavy bleeding, severe pelvic pain, bleeding after sex, or a persistent change in your usual cycle. Period-delay medicine should not be used to cover up a symptom that needs investigation.