Norethisterone: side effects, risks, and benefits

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What is norethisterone? | How does norethisterone work? | Who can use norethisterone? | What are the benefits of norethisterone? | Side effects of norethisterone | How should I take norethisterone?

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Using norethisterone for menorrhagia (heavy bleeding) | Should I take norethisterone? Women’s experiences | Is it possible to delay your period? Myths vs facts

You may have heard of norethisterone — a synthetic hormone commonly found in contraceptive pills — and wonder whether it is right for you. This article aims to give you some information that may help you make that decision.

Norethisterone is a hormone belonging to a group called progestins, which are artificial forms of progesterone— a hormone that is found naturally within our bodies.

There are different preparations of norethisterone that can be used in different doses, which depend on what you are using it for.

Commonly, norethisterone is used in the progestogen-only contraceptive pill, which is also known as the “mini-pill”. Noriday is an example of a progesterone-only contraceptive pill containing norethisterone.

Norethisterone can also be used in combination with oestrogen in the combined oral contraceptive pill. When used in contraception, norethisterone works towards preventing pregnancy, controlling menstruation, and helping to manage endometriosis pain.

On its own, norethisterone 5mg tablets can be used taken to delay periods, which may be desirable if you are planning a holiday or have a sporting event coming up where you’d rather not have to worry about your period. It is important to remember that when taken as a 5mg tablet, norethisterone is not strong enough to act as a contraceptive, so you will need to use alternative forms of contraception.

Using norethisterone in contraception

When norethisterone is used in contraceptive pills, one way it works to prevent pregnancy is by suppressing a part of the brain called the pituitary gland where essential sex hormones — follicular stimulating hormone (FSH) and luteinising hormones (LH) — are released. These hormones are required for ovulation, so if they are not released, no egg is available to be fertilised. However, if you take the progesterone-only pill, FSH and LH are not always fully suppressed, and so ovulation can still sometimes happen. It is estimated that around 50% of people with wombs who take the mini pill still ovulate.¹

Norethisterone may also be used to reduce period pain and to make periods lighter

Another way that norethisterone works to prevent pregnancy is by thickening the cervical mucus, which makes it difficult for sperm to swim into the womb to be fertilised. The thickened mucus also slows down the movement of the egg as it travels down the Fallopian tubes.

Finally, progestins work to thin the womb lining, making it difficult for the fertilised egg to implant successfully.

Norethisterone for period delay

Period delay is a common reason for using norethisterone, particularly if you’re going on holiday and would rather not experience your monthly bleed while away. It is generally safe to use norethisterone for this purpose, however, be sure to seek advice from your doctor as there are some instances where using norethisterone isn’t advisable (for example, if you have porphyria or are being treated for breast cancer).

Norethisterone works to delay periods by keeping the levels of progesterone high. Since the lining of the womb sheds once progesterone levels fall, keeping these levels high can result in lighter or delayed periods.

Other effects of norethisterone on periods

Norethisterone may also be used to reduce period pain and to make periods lighter.

It is thought that norethisterone helps manage period pain because it thins the lining of the womb but also stabilises it and prevents it from shedding, which has been shown to help with endometrial pain.² The lining of the womb being thin means that menstrual bleeding is usually less heavy, although this effect is variable in different people. In addition, period pain is worse during ovulation, therefore by preventing ovulation from occurring it follows that norethisterone can lessen period pain.

Progesterone-only pills like norethisterone have in the past been used to help with PMS (pre-menstrual syndrome), but norethisterone is not recommended for treatment of PMS any longer.³ If you have PMS, you should speak to your doctor about other options for managing PMS, like combined (oestrogen and progesterone) contraceptive pills.

Norethisterone is suitable for most people who menstruate, however there are some instances in which it wouldn’t be safe to take. For example, it is not advised to take norethisterone if you might be pregnant, however no adverse effects have been shown for either parent or baby when conception has happened while using the mini pill.

People who are in the active stages of breast cancer (generally within first 5 years of diagnosis) are not advised to use norethisterone due to concerns that it might make the cancer worse, unless progestogens are being used as part of their treatment.⁴ It is also not advised for those who have a history of breast cancer, however norethisterone can be used if there is no evidence of disease after five years and if using non-hormonal contraceptives (like the copper IUD) is not an option.

If you have undiagnosed abnormal periods, it is best that your doctor first investigates the cause of your irregular bleeding before advising on whether norethisterone is a possible course of action

If you have, or you think you may have breast cancer, you doctor will be able to advise on whether norethisterone is suitable for you.

People with benign or malignant liver tumours, severe cirrhosis, or acute liver disease should avoid norethisterone because the liver is linked, in rare cases, to liver problems.⁵

If you have undiagnosed abnormal periods, it is best that your doctor first investigates the cause of your irregular bleeding before advising on whether norethisterone is a possible course of action. This is because irregular bleeding may be due to many causes, some of which require further medical investigations like a vaginal ultrasound scan.

Those who are taking other medications, such as drugs used for epilepsy, should consult a healthcare professional before starting the progesterone-only pill. Some medications can interact with norethisterone and decrease its effectiveness, which is particularly important if norethisterone is being used to prevent pregnancy.

The mini pill can be useful for people who cannot take contraception that contains oestrogen, such as the combined pill. This includes those who:

• Have a very high risk of blood clots, or have multiple risk factors for heart disease such as smoking, being in an older age group, diabetes, or high blood pressure
• Have a known history of stroke or heart disease, current breast cancer, or migraine with sensory symptoms

Taking oestrogen could make these medical conditions worse or increase the risk of them.

The most recent evidence suggests that there is no increased risk of developing blood clots or having a stroke whilst taking progesterone-only pills like norethisterone.⁶ However, you should always speak to your doctor to understand any risks particular to you before taking norethisterone.

Another advantage of the mini pill is that once stopped, fertility returns quickly, which is good news if you have come off contraception because you want to get pregnant.

As with all medications, taking norethisterone can be associated with side effects. When taken as contraception, one of the most common side effects is irregular periods, which is a common reason for stopping. Irregular bleeding can vary from stopping completely⁷ to prolonged bleeding, breakthrough bleeding, or spotting in one or more cycles in up to 70% of people who menstruate.⁸

Progesterone-only contraceptive pills containing norethisterone should be taken every day and ideally at the same time each day. This is because the hormone does not last long in the blood stream

The mini pill can cause breast tenderness in some people, which may be due to extra stimulation of the hormones in the breast tissue. Studies have also shown that people who use the mini pill develop more cysts in their ovaries compared with those who are not taking the pill. In general, these do not lead to any problems unless it causes pain, and if this is the case, then it may be worthwhile to change to a different contraception.⁹

There have been reports of some having worse acne flares when they are on the mini pill. This may be related to progesterone stimulating the sweat glands and increasing sebum secretion, therefore causing acne.¹⁰ It is not known who will experience certain side effects more than others.

There is no scientific evidence that mini pills will make you gain weight.¹¹ It is uncertain whether it affects depression,¹² and it has not been found to increase in frequency of headaches,¹³ but these symptoms have been reported.

Norethisterone has not been associated with serious complications. Overall, using norethisterone in the mini pill reduces the risk of ectopic pregnancies (pregnancies outside of the womb) because it prevents pregnancy overall. But if pregnancy does occur, then the likelihood of pregnancy being ectopic is higher than if that person is not taking any contraception.¹⁴ At the moment, there is no evidence that using norethisterone in the mini pill increases breast cancer risk.¹⁵

The mini pill also does not prevent sexually transmitted diseases, so it is worth using a condom for this additional protection.

Progesterone-only contraceptive pills containing norethisterone should be taken every day and ideally at the same time each day. This is because the hormone does not last long in the blood stream. It needs to be taken daily to stop any hormone-free days. If you miss the pill by more than 3 hours, it is advised that extra contraception such as use of condom is used in the meantime for the next 2 days whilst the routine is re-started.

If norethisterone 5mg tablets are used for period delay, then it should be taken three times a day, and you should start taking it three days before the expected start of your period. When norethisterone is stopped, periods will usually begin 2-3 days after.

It is important to remember that there are different preparations of norethisterone and the dose used may be different, so norethisterone used to delay periods or used to prevent bleeding may not have an effective contraceptive effect. If you wish to prevent pregnancy whilst taking norethisterone, then it is important to use additional alternative forms of contraception.

Featured image is of a three pill packets, arranged in a row against a bright yellow background

Last updated February 2023
Next update due 2026