Tamoxifen is a hormonal therapy drug used to treat breast cancer. It's sometimes used to treat other cancers and conditions. It’s best to read this with our general information about breast cancer.

You usually have tamoxifen as tablets and as an outpatient. Your cancer doctor or nurse will tell you how long you take it for.

Like all hormonal therapy drugs, tamoxifen can cause side effects. Some of these can be serious, so it’s important to read the detailed information below. How hormonal therapy affects people varies from person to person. Your doctor or nurse can talk to you more about this and give you advice on how to manage side effects.

Tell your doctor or nurse straight away if you feel unwell or have severe side effects, including any we don’t mention here. If you need to see a health professional for any reason other than cancer, always tell them that you are having this treatment.

How tamoxifen works

Hormones are substances produced naturally in the body. They act as chemical messengers and help control the activity of cells and organs. Hormonal therapies are drugs that interfere with the way hormones are made or how they work in the body.

Many breast cancers rely on the hormone oestrogen to grow. This type of breast cancer is called oestrogen receptor-positive (ER-positive) breast cancer. Tamoxifen blocks oestrogen from reaching the cancer cells. This means the cancer may grow more slowly or stop growing altogether.

When tamoxifen is given

Tamoxifen is used to treat ER-positive breast cancer. It may be given to:

Sometimes tamoxifen is also given to:

  • treat other types of cancer
  • treat or prevent breast tenderness and swelling (gynaecomastia) – this can be a side effect of some hormonal therapies used for prostate cancer.

Taking your tamoxifen

Tamoxifen is usually taken as a tablet once a day. You take it at the same time each day, morning or evening. It is also available as a syrup. Always take tamoxifen exactly as your nurse or pharmacist explained. This is important to make sure it works as well as possible for you.

Here are some important things to remember:

  • If you forget to take tamoxifen, take it as soon as you remember. But if it’s almost time for your next dose, don’t take a double dose. Just take the next dose at your usual time.
  • Keep the tablets or syrup in their original packaging and at room temperature, away from heat and direct sunlight.
  • Keep tamoxifen safe and out of the sight and reach of children.
  • Get a new prescription before you run out of tamoxifen and make sure you have plenty for holidays.
  • Return any remaining tamoxifen to the pharmacist if your treatment is stopped.

Possible side effects of tamoxifen

We explain the most common side effects of tamoxifen here. We also include some rarer side effects. You may get some of the side effects we mention, but you are very unlikely to get all of them. If you are having other drugs as well, you may have some side effects that we don’t list here.

You will see a doctor or nurse regularly while you have this treatment. Always tell your doctor or nurse about any side effects you may have. They can prescribe drugs to help control them and give you advice about managing them. Don’t stop taking tamoxifen without talking to your doctor first.

More information about this drug

We are not able to list every side effect for this treatment here, particularly the rarer ones. For more detailed information, you can visit the electronic Medicines Compendium (eMC).

Hot flushes and sweats

These are common and are often mild, but this can vary. Hot flushes and sweats may lessen after the first few months. Some people continue to have them for as long as they take tamoxifen.

There are things you can do to try to reduce flushes:

  • Try to cut down on nicotine, alcohol and hot drinks containing caffeine, such as tea and coffee.
  • Dress in layers, so you can remove clothes as needed.
  • Wear clothes made from natural fabrics, such as cotton.

If hot flushes are troubling you, tell your doctor or nurse. Low doses of certain anti-depressant drugs can help to reduce flushes.

Women can read more about coping with hot flushes in our section on managing menopausal symptoms.

Men can read more about coping with hot flushes in our section on managing hormonal symptoms.

Vaginal effects

These can include discharge, itching and dryness. Non-hormonal creams, gels or lubricants can help to reduce vaginal dryness and any discomfort during sex. You can buy these at a chemist or your doctor can prescribe them.

Change in periods

If you are still having periods, they may become irregular, lighter or sometimes stop altogether.

Loss of sex drive

Your sex drive may be lower while taking tamoxifen. Talk to your doctor or nurse for advice.

We have more information about coping with the effects of treatment on your sex life.

Feeling sick (nausea) and indigestion

Any sickness usually improves after a few weeks. Try taking tamoxifen with food or at night.

Let your doctor or nurse know if you continue to feel sick, or if you have indigestion. They can give you advice or prescribe drugs to help.

Eye problems

Tamoxifen may cause cataracts (clouding of the lens of the eye) or other eye problems. If you get blurry vision or notice any change in your vision, always tell your doctor or nurse.


If you have headaches, let your doctor or nurse know. They can usually be controlled with mild painkillers.

Effects on the nervous system

Tamoxifen can affect the nervous system. You may have pins and needles, or feel tingling in your arms and legs. You may also feel dizzy or unsteady, or have taste changes. Tell your doctor or nurse if you notice any of these symptoms.

It is important not to drive or operate machinery if you feel dizzy.

Leg cramps and muscle pain

Walking may stretch the muscles and help with this. Let your doctor or nurse know if leg cramps or muscle pains are a problem.

Tiredness and lack of energy

You may feel tired, sleepy or feel you have no energy when you start taking tamoxifen. Try to pace yourself until this improves. Aim for a balance between having enough rest and being physically active. Doing exercise, like going for regular short walks, will help you to feel less tired.

It is important not to drive or use machinery if you feel sleepy.

Skin rashes

You may get a mild skin rash while taking tamoxifen. Tell your doctor or nurse if this happens.

It is very important to contact your doctor straight away if you get a severe skin rash.

Hair thinning

Your hair may become thinner while taking tamoxifen. This is usually mild. Your hair will get thicker after treatment finishes.

Weight gain

You may put on weight when you are taking tamoxifen. Eating healthily and being more physically active can help to keep you to a healthy weight. Your doctor or nurse can give you more advice.

Changes in mood and concentration

Some people have mood changes or feel low or depressed when taking tamoxifen. You may also find it harder to think clearly or to concentrate.

Let your doctor or nurse know if this is a problem, especially if you feel low most of the time or think you may be depressed.

Less common side effects of tamoxifen

Blood clots (thrombosis)

Tamoxifen can increase your chances of getting a blood clot. Let your doctor or nurse know if you have ever had a blood clot or deep vein thrombosis (DVT).

A blood clot can cause:

  • pain, redness and swelling in a leg or arm
  • breathlessness and chest pain.

Contact your doctor straight away if you have any of these symptoms.

A blood clot is serious but your doctor can treat it with drugs that thin the blood. Your doctor or nurse can give you more information.

Tumour flare

If you take tamoxifen for cancer that has spread to the bones, you may get pain in your bones when you start taking it. This is sometimes called tumour flare.

Increased risk of womb cancer

Women who have been through the menopause and take tamoxifen for a long time have a higher risk of womb cancer. But the benefits of tamoxifen outweigh this risk. If you have been through the menopause, always tell your doctor if you have any bleeding from the vagina.

You should also tell them if you have any discomfort in the lower tummy (pelvis), such as pain or pressure. These can be early signs of womb cancer, although they are usually caused by other conditions. If womb cancer is found early, treatment can be very successful.

Side effects can usually be controlled or improved. Always let your doctor or nurse know about any side effects you have so they can help you feel better.

Other information about tamoxifen

If you have ongoing side effects

Most of the time side effects can be controlled or managed. But for a few people, they can be more troubling. If this happens, make sure you talk to your doctor or nurse. They can usually suggest ways to improve your side effects. If things don’t improve, go back to your doctor or nurse. They may suggest you try something else.

It is really important not to stop taking tamoxifen without telling your doctor, as this may affect the success of your treatment. If side effects can’t be managed, your doctor may suggest you take a different type of hormonal therapy.


Your doctor will advise you not to become pregnant when you’re taking tamoxifen. This is because tamoxifen may harm a developing baby. For women, it is important to use an effective, non-hormonal form of contraception during treatment and for a few months after it finishes.

Even if your periods have stopped or are irregular, you still need to use contraception. Your doctor or nurse can tell you more about this.


Women who have not been through the menopause may still be able to get pregnant after treatment. But some women go through their natural menopause during treatment.

Doctors usually advise you to wait for a few months after tamoxifen treatment finishes before you try to get pregnant. Talk to your doctor first if you are thinking of trying to become pregnant.

Other medicines

Tamoxifen can interact with other drugs. For example, it can increase the effect of a blood-thinning drug called warfarin. Let your doctor know straight away if you are taking warfarin or any other drugs. Some other drugs may make tamoxifen less effective.

Tell your doctor about any medicines you are taking, including ones you can buy yourself, complementary therapies and herbal drugs.


Tamoxifen syrup (Soltamox) contains alcohol. Tell your doctor, nurse or pharmacist if this is a problem for you. This may affect your ability to drive or operate machinery.

Problems with lactose

Tamoxifen syrup (Soltamox) contains a type of sugar called lactose. If you have been told by a doctor that you cannot digest lactose (lactose intolerant) or other sugars, talk to your doctor before taking this drug.

Medical or dental treatment

If you need to go into hospital for any reason, always tell the doctors and nurses that you are taking tamoxifen. Explain you are taking a hormonal therapy drug that no one should stop or restart without checking with your cancer doctor first. Tell them the name of your cancer doctor and their contact details so they can ask for advice.

Always tell your dentist you are taking tamoxifen before having any dental treatment.