Sometimes a period is simply badly timed — landing on a holiday, a wedding, a sporting event or an important set of exams. In the UK, one recognised option to move it is a short course of period delay tablets. The most commonly prescribed is norethisterone. This article explains how it works, when it is started and stopped, the side effects and cautions to be aware of, and what a clinician will check before prescribing it.
When period delay is considered
Delaying a period is a lifestyle choice rather than a medical necessity, and it is entirely reasonable to want to do it for a specific occasion. People most often ask about it before travel, holidays, competitions, religious events or times when a period would be especially inconvenient or uncomfortable. It is a short-term measure for a one-off event, not a way to manage periods long term — if your periods are consistently heavy, painful or disruptive, that is worth a separate conversation with a clinician, as there may be more suitable ongoing options.
It is also worth knowing that if you already take a combined contraceptive pill, you may be able to delay your period simply by running two packets together and skipping the usual pill-free break, rather than needing a separate medicine. That option is not suitable for everyone and is not how the progestogen-only pill works, so it is always worth checking with a clinician or pharmacist first. For people who are not on the combined pill, or who cannot use that approach, a dedicated period delay tablet is the usual route.
How norethisterone delays a period
To understand how the tablets work, it helps to know what triggers a period. During the natural cycle, the lining of the womb (the endometrium) builds up under hormonal influence. Towards the end of the cycle, levels of the hormone progesterone fall, and that drop is the signal for the lining to break down and shed — which is your period.
Norethisterone is a synthetic progestogen, meaning it behaves like the body's own progesterone. Taken as a course, it keeps progestogen levels artificially raised so the expected natural drop does not happen. Without that fall in hormone, the womb lining is held in place rather than shed, and the period is postponed. Once you stop the tablets, hormone levels fall as they normally would, and the period follows within a few days.
When to start and how long it can be used
Norethisterone for period delay is typically started around three days before your period is expected. Because it works by maintaining hormone levels, it needs to be in your system before the natural hormone drop would otherwise begin — starting too late means the period may already have been triggered. It is then taken regularly, usually a few times a day as directed, for the duration you need the delay.
The delay lasts only as long as you keep taking the tablets, and there is a sensible limit on how long a course should run. Clinicians generally keep these courses short, and the exact number of days will be set out for you. This is not a medicine to take continuously or repeatedly without review, which is one reason it is prescribed rather than bought off the shelf. Knowing your usual cycle length helps a clinician time the course accurately, so it is worth having that information to hand.
Planning ahead makes a real difference. Because the tablets need to be started a few days before your period is due, leaving it until the last minute — or until bleeding has already begun — usually means it is too late for that cycle. If you know an important event is coming up, it is best to arrange a consultation in good time so the course can be timed properly and you are not left rushing. Having a note of when your last period started, and roughly how many days your cycle usually runs, allows a clinician to work out the right start date with you.
What to expect once you stop
When you finish the course, hormone levels fall in the way they naturally would, and your period usually arrives within a couple of days. That first bleed is simply the delayed period arriving, and it is nothing to be concerned about. Occasionally people notice some light spotting while still taking the tablets, particularly towards the end of a longer course, which is generally not a cause for worry but is worth mentioning at any follow-up. Your next cycle should then return to its usual rhythm, though it can take a cycle or two to feel completely back to normal.
It does not work as contraception
An important point that often surprises people: norethisterone used in this way, at period-delay doses, is not licensed or reliable as contraception. It is a different use, and a different dosing pattern, from progestogen-based contraceptive pills. If you need contraception, you should continue your usual method — or use condoms — while taking period delay tablets. If you are choosing a regular method, our comparison of combined and progestogen-only contraception may be a helpful starting point for that separate conversation.
Side effects, contraindications and clinical cautions
Most people tolerate a short course well, but because norethisterone is a hormone, it can cause side effects. Commonly reported ones include bloating, breast tenderness, nausea, headaches, mood changes and a reduced sex drive. These are usually mild and settle once the course finishes.
More importantly, period delay tablets are not suitable for everyone. A personal history of blood clots — venous thromboembolism such as a deep vein thrombosis or pulmonary embolism — is a specific caution referenced in the BNF, and other factors such as certain liver conditions, some cancers, and particular cardiovascular risks may also make norethisterone inappropriate. This is exactly why a clinical review matters: what looks like a simple convenience medicine still has a genuine safety profile that has to be matched to your individual health.
Norethisterone can also interact with other medicines, and some conditions call for extra caution rather than an outright no. That is why a clinician will ask about your full medical history and everything you take, including anything bought over the counter or any herbal remedies, before deciding whether it is a reasonable option. If period delay is not appropriate for you on this occasion, that is not the end of the conversation — a clinician can explain why and, where relevant, discuss alternatives that might achieve what you need more safely.
What a clinician will check before prescribing
A period delay consultation is usually quick but thorough. A clinician will typically ask about your medical history, any history of clots or clotting disorders in you or close family, your current medicines, whether you smoke, and the dates and length of your usual cycle so the course can be timed correctly. They will also confirm you are not pregnant and talk through what to expect, including the return of your period after stopping.
From there, if norethisterone is appropriate, they can advise on dose, when to start, and how long to continue. If it is not suitable for you, they can discuss alternatives. The goal is simple: to help you move a period safely, with the reassurance that a UK-registered clinician has checked it is a reasonable option for you rather than assuming one size fits all.