| TL;DR Norethisterone is a synthetic progestogen and the only medication licensed in the UK specifically for period delay. Most women tolerate it well, particularly when used for short courses. Common side effects — including breakthrough bleeding, breast tenderness, nausea, headaches, and mood changes — are generally mild and resolve once the course ends. The most significant serious risk is a small but real increase in the chance of blood clots (VTE), which is why a clinical assessment before prescribing matters. Norethisterone is not suitable for everyone — women with a history of blood clots, breast cancer, active liver disease, migraine with aura, or undiagnosed vaginal bleeding should not take it. |
Norethisterone is one of the most commonly prescribed medications in UK for women’s health, taken by hundreds of thousands of women every year, predominantly to delay a period for a holiday, wedding, or important event. Despite how widely it is used, the side effect information that most women receive at the point of prescription is often incomplete. The common side effects are mentioned briefly. The serious ones — particularly the blood clot risk and the mental health effects — are frequently skimmed or omitted entirely. This guide covers the full picture, grounded in the current prescribing evidence and patient information, so you can make a genuinely informed decision.
What Is Norethisterone and How Does It Work?
Norethisterone is a synthetic progestogen, a laboratory-made version of the natural hormone progesterone. Norethisterone is the only progestogen licensed in the UK to delay periods. Norethisterone 5mg three times a day is the licensed dose, and to be effective, it should be started at least 3 days before the expected period.
It works by maintaining artificially elevated progesterone levels. Normally, your period starts when progesterone levels fall — triggering the shedding of the womb lining. Norethisterone prevents that fall, keeping the lining in place and delaying the bleed. Periods usually resume within 3 days of discontinuing norethisterone.
In the UK, norethisterone is prescribed not only for period delay but also for heavy or painful periods, endometriosis, and premenstrual syndrome. The dose and duration differ significantly depending on the indication — the 5mg three-times-daily dose for period delay is much higher than doses used in other contexts, which is relevant when considering side effect risk.
One important pharmacological detail that is rarely explained to patients: norethisterone is partly converted in the body to ethinylestradiol — a synthetic oestrogen. This is why the safety guidance around norethisterone, particularly regarding blood clots, is broadly similar to the guidance for the combined contraceptive pill rather than a purely progestogen-only product. It is a detail that significantly shapes the contraindications.
Common Norethisterone Side Effects
These are the side effects that affect a meaningful proportion of women taking norethisterone. They are generally not serious and typically resolve once the course ends, but they are worth knowing about before you start.
Breakthrough Bleeding and Spotting
This is the most frequently reported side effect. Changes in bleeding pattern are one of the most visible effects of norethisterone — depending on the dose and indication, women may experience irregular spotting or breakthrough bleeding between periods, particularly when taking norethisterone for period delay. For some women taking norethisterone to delay a period, the tablet does not suppress bleeding entirely — particularly if the course is started fewer than three days before the expected period, or if the dose is missed or taken inconsistently.
The longer you delay your period — up to the maximum of 27 days — the more likely you are to experience side effects, including spotting and irregular bleeding.
Breast Tenderness
Soreness or heaviness in the breasts is a common hormonal effect of progestogen. It is generally mild and resolves when the course ends. If breast changes persist after stopping norethisterone, or if you notice any lumps, dimpling, or nipple changes, see your GP promptly — unrelated to norethisterone, these warrant assessment.
Headaches
Headaches are a commonly reported side effect of norethisterone. For most women they are mild and manageable with standard pain relief such as paracetamol. However, there is an important distinction to make here — covered in the serious side effects section below — regarding new or unusually severe headaches, which can be a warning sign of a serious complication and require you to stop the medication immediately.
Nausea and Stomach Discomfort
Stomach discomfort, nausea and vomiting are recognised side effects of norethisterone. Taking it after food can reduce these effects. For most women, nausea is mild, particularly on short courses, and improves after the first few days.
Low Mood and Mood Changes
This is one of the most clinically significant common side effects, and the one most frequently underemphasised at the point of prescribing.
The norethisterone patient information leaflet warns that norethisterone tablets have been associated with reported depression or depressed mood, noting that depression can be serious and may sometimes lead to suicidal thoughts, and advising patients to contact their doctor for further medical advice as soon as possible if they experience mood changes and depressive symptoms.
People with a history of depression, anxiety or premenstrual mood problems may be more sensitive to mood-related side effects of norethisterone. If you notice persistent low mood, loss of interest in things you usually enjoy, increased anxiety, or thoughts of self-harm or suicide, you should contact a healthcare professional promptly.
This is not a reason to avoid norethisterone if it is otherwise suitable for you. It is a reason to monitor your mood during the course, mention any history of depression or premenstrual dysphoric disorder (PMDD) when requesting it, and know that stopping the medication is appropriate and available if these effects occur.
Reduced Sex Drive
A reduction in libido is a recognised hormonal side effect. It is generally temporary and resolves after stopping the course.
Weight Changes
Slight weight fluctuation is a common side effect of norethisterone, typically related to fluid retention rather than fat accumulation. Significant weight gain is not a well-established effect of short-course norethisterone, though women using it long-term for other indications may notice more pronounced changes.
Acne
Norethisterone has mild androgenic (testosterone-like) properties, which in some women can contribute to acne or worsen existing skin breakouts. In a clinical study of women using 5mg/day norethisterone for endometriosis, acne was reported in 9.9% of patients over a median treatment duration of 13 months. For short-course period delay, acne is less commonly a concern.
Serious Norethisterone Side Effects
These side effects are rare but require you to stop norethisterone immediately and seek urgent medical attention.
Blood Clots (Venous Thromboembolism — VTE)
This is the most significant serious risk associated with norethisterone, and it deserves a clear, honest explanation rather than a brief mention.
A review of the latest evidence by the MHRA confirmed that combined hormonal contraceptives containing levonorgestrel, norethisterone, or norgestimate have the lowest risk of VTE among combined hormonal contraceptives, and that the benefits of any combined hormonal contraceptive far outweigh the risk of serious side effects. The excess VTE risk associated with norethisterone-containing contraceptives is approximately 10 to 15 additional cases per 100,000 women per year compared with non-use — a low absolute risk, but one that becomes clinically significant in women who already have elevated baseline VTE risk factors.
The risk factors that increase the relevance of the VTE concern include: a personal or family history of blood clots, obesity (BMI above 30), smoking — particularly in women over 35 — prolonged immobility such as a long-haul flight, recent surgery, and conditions such as thrombophilia or antiphospholipid syndrome.
Previous VTE, migraines with aura, and uncontrolled hypertension are contraindications to certain progestogens including norethisterone. Severe obesity, defined as BMI above 30kg/m², is a risk factor for VTE and should be considered when prescribing.
Symptoms of a blood clot that require you to call 999 or go to A&E immediately:
- Sudden pain, swelling, or redness in a leg or calf
- Chest pain or tightness
- Sudden breathlessness
- Coughing up blood
- Sudden severe headache, vision changes, or one-sided weakness or numbness
Blood clots are a rare side effect of norethisterone. Stay active and well hydrated while you take this medicine, particularly important during travel or periods of reduced movement.
Severe or New Migraines
If you experience a first-ever migraine while taking norethisterone, or a migraine that is significantly worse than any you have had before, stop taking it immediately and contact your GP. If it is your first-ever migraine, or it is worse than any you have had before, stop taking norethisterone and speak to your prescriber or GP straight away for advice. New neurological symptoms during norethisterone use — including visual disturbances, facial numbness, or speech difficulties — should be treated as a medical emergency.
Liver Problems
Cholestasis — a condition where bile flow from the liver is reduced or blocked — is a rare but recognised side effect of norethisterone. Symptoms include severe itching (usually without a rash), dark urine, jaundice (yellowing of the skin or eyes), and pale stools. If these occur, stop norethisterone and seek urgent medical advice.
Who Should Not Take Norethisterone
This section is critically important and is one of the most frequently underexplained aspects of norethisterone prescribing.
Absolute Contraindications — Do Not Take Norethisterone If You Have:
- A personal history of blood clots (DVT or pulmonary embolism)
- Current or recent breast cancer — if you have breast cancer, or have had it in the past, you should not take norethisterone. Like the combined contraceptive pill, it slightly increases the risk of breast cancer, and this risk rises the longer you take it. Active liver disease or a history of liver tumours
- Undiagnosed vaginal bleeding
- Porphyria (a rare metabolic condition)
- Pregnancy
Conditions Requiring Extra Caution:
- Migraine — women with a known history of migraine with sensory symptoms should not take norethisterone without careful clinical assessment.
- Diabetes — norethisterone can affect glucose tolerance and should be used with caution
- Uncontrolled high blood pressure
- Epilepsy — certain anti-epileptic medications can affect how norethisterone is metabolised
- Severe obesity (BMI above 30)
- Active smokers over the age of 35
The NHS Specialist Pharmacy Service guidance on choosing a medicine to delay periods provides detailed prescribing considerations and notes that norethisterone is not always the most appropriate choice — alternatives exist and should be discussed with your prescriber.
Norethisterone Is Not a Contraceptive
This point causes real-world harm when it is not communicated clearly. The individual should be advised that norethisterone is not a contraceptive and so another form of contraceptive should be used to avoid pregnancy.
Many women assume that a hormone tablet that delays menstruation must also prevent pregnancy. It does not. If you are sexually active and not using contraception, you can become pregnant while taking norethisterone. If your period does not arrive within three to four days of stopping your course, take a pregnancy test.
What Happens After You Stop Norethisterone
Understanding what to expect when a course ends helps prevent unnecessary alarm.
Period Timing
Periods usually resume within 3 days of discontinuing norethisterone. Some women experience a slightly heavier or more intense bleed than usual for their first period back — this is the womb lining shedding after a longer delay, not a sign of a problem. If no period arrives within seven days of stopping, take a pregnancy test and contact your GP if the result is negative.
Side Effect Resolution
For most people, side effects are temporary and will clear up once you stop taking norethisterone. Mood changes, breast tenderness, nausea, and headaches typically resolve within days of finishing the course. Breakthrough bleeding that has occurred during the course will also resolve.
Fertility
Norethisterone does not affect long-term fertility. Your natural menstrual cycle and ovulation will resume normally after the course ends.
Practical Tips for Reducing Side Effect Risk
These are small but meaningful practical steps that reduce the likelihood of side effects during a norethisterone course.
Take it with food. Nausea is reduced significantly when norethisterone is taken with a meal rather than on an empty stomach.
Take it at consistent times. Taking medication at the same time every day avoids large changes in hormone levels, which can contribute to mood changes. Set a reminder for each of your three daily doses.
Stay active and hydrated. Physical movement and good hydration reduce the already small VTE risk during the course — particularly important if you are taking norethisterone during or around air travel.
Monitor your mood. Tell someone you trust that you are taking norethisterone, so they can flag any mood changes you might not notice yourself. If you have a history of depression, PMDD, or anxiety, discuss this with your prescriber before starting.
Start on time. Beginning the course fewer than three days before your expected period significantly reduces its effectiveness and can result in the period starting despite the medication — causing breakthrough bleeding rather than a clean delay.
Alternatives to Norethisterone for Period Delay
Norethisterone is the only medication licensed in the UK specifically for period delay. However, for women who are unsuitable candidates for norethisterone — or who prefer an alternative approach — there are other options worth knowing about.
Taking the Combined Pill Back-to-Back
Women already prescribed a monophasic 21-day combined oral contraceptive pill can take it back-to-back without a break, skipping the pill-free week and therefore the withdrawal bleed. The combined oral contraceptive pill is an alternative to norethisterone for period delay. Monophasic 21-day pills can be used continuously for period delay, though this should be discussed with a pharmacist, contraceptive service, or doctor as it varies depending on the pill being taken.
Medroxyprogesterone
Medroxyprogesterone is sometimes used off-label for period delay when norethisterone is not suitable. It requires a clinical discussion as it is not the licensed choice for this indication.
For women looking to explore period delay options, our women’s health services at Star Pharmacy offer confidential consultations with registered prescribers who can assess which approach is most appropriate for your individual health history. If norethisterone is suitable for you, we provide discreet UK delivery to your door.
Final Thoughts
Norethisterone is a well-established, widely used medication that works effectively for the majority of women who take it for short-term period delay. The side effects that most women experience — if they experience any at all — are mild and resolve quickly. Understanding the serious risks, particularly the blood clot risk and the mental health effects, is not about making norethisterone seem dangerous — it is about being able to use it safely and knowing when to stop.
The key is an honest prescribing consultation that matches the medication to the individual. Not everyone is a suitable candidate, and for those who are, understanding what to expect makes the difference between a straightforward course and an unnecessarily alarming experience.
If you would like to explore norethisterone or other period delay options, our team at Star Pharmacy offers confidential women’s health consultations with registered prescribers. We will assess your suitability thoroughly, explain what to expect, and arrange discreet, fast delivery across the UK. You can also contact our pharmacist team directly with any questions before requesting treatment.
FAQs
What are the most common side effects of norethisterone?
The most commonly reported norethisterone side effects are breakthrough bleeding or spotting, breast tenderness, headaches, nausea, and mood changes, including low mood or irritability. Side effects from norethisterone are unusual but can include spotting, irregular bleeding, sore breasts, stomach ache, and a lower sex drive. The majority of these are mild, temporary, and resolve within days of stopping the course. If side effects are severe, persistent, or significantly affecting your daily life, stop the medication and contact your GP or pharmacist.
Does norethisterone cause weight gain?
It can cause a small, temporary increase in weight due to fluid retention, but significant or permanent weight gain is not a well-established effect of short-course norethisterone. Slight weight fluctuation is possible and is typically related to hormonal fluid changes rather than fat gain. Women using norethisterone long-term for conditions such as endometriosis may notice more pronounced changes, which are worth discussing with the prescribing clinician.
Can norethisterone affect your mood?
Yes, mood changes, including low mood, irritability, and anxiety, are a recognised norethisterone side effect. The patient information leaflet specifically notes the risk of depression, including serious depression, and advises women to contact a doctor if these symptoms develop. Women with a personal history of depression, anxiety, or PMDD are more sensitive to this effect and should mention it when requesting norethisterone. If you experience persistent low mood or any thoughts of self-harm while taking it, stop the medication and contact your GP without delay.
Is norethisterone safe for everyone?
No, norethisterone is not suitable for everyone. Women with a personal history of blood clots, breast cancer, active liver disease, migraine with aura, undiagnosed vaginal bleeding, or porphyria should not take it. Previous VTE and migraines are contraindications to norethisterone, and severe obesity is a significant risk factor that must be considered at the point of prescribing. A clinical assessment before prescribing exists for this reason — it is not a formality. For personalised advice on whether norethisterone is suitable for you, speak to our pharmacy team at Star Pharmacy or consult your GP.
What should I do if I get side effects from norethisterone?
For mild side effects — nausea, breast tenderness, mild headaches, spotting — continue the course as prescribed unless they become unmanageable. Taking norethisterone with food reduces nausea. For mood changes that feel significant or persistent, stop the medication and contact your GP. For any symptoms that could indicate a blood clot — leg pain or swelling, chest pain, breathlessness, sudden severe headache, or vision changes — stop immediately and call 999 or go to A&E. The NHS guide on norethisterone and period delay provides further information on when to seek help.
Will my period be normal after norethisterone?
Your first period after norethisterone may be slightly heavier or more prolonged than usual — this is the womb lining shedding after a longer delay and is not a cause for concern. Subsequent periods return to your normal pattern. If no period arrives within seven days of stopping, take a pregnancy test. If periods remain irregular or absent beyond two cycles, speak to your GP.