Tamoxifen is a hormone therapy used to treat breast cancer. It is also occasionally used to treat other types of cancer.

Tamoxifen can be used to treat or prevent tenderness or swelling of the breasts—two side effects of some hormone therapies used in men with prostate cancer.


Hormones are substances produced naturally in the body. These act as chemical messengers and help control the activity of cells and organs. Hormone therapies interfere with the way hormones are made or formed in the body.

Many types of breast cancer depend on the hormone estrogen to grow. This type of breast is called estrogen receptor-positive (ER-positive) breast cancer. Tamoxifen blocks estrogen from reaching the cancer cells. This means the cancer grows more slowly or stops growing altogether.


Tamoxifen is only effective in people who have hormone-positive breast cancer. It is the main hormone therapy drug given to women who have not gone through menopause. Sometimes, it is also given to women after menopause.

Tamoxifen is used after surgery and other treatments to reduce the risk of breast cancer returning. It also lowers the risk of developing cancer in the other breast. Tamoxifen is normally taken over five years or more. Some studies show that taking the drug over 10 years can further reduce the risk of the cancer coming back. Alternatively, women can have tamoxifen for two or three years and then change to a different kind of hormone therapy.

Tamoxifen is occasionally used before surgery to reduce large cancers in order to eliminate the need for a mastectomy.

Tamoxifen is also used to control breast cancer that has returned or has spread to other parts of the body (secondary breast cancer).


Tamoxifen is taken in pill form, normally once a day. The pills are taken at the same time each day, either in the morning or at night. It is also available as a sugar-free syrup. Always take the pills exactly as your nurse or pharmacist has told you. This is important to ensure that it is working as well as possible.

  • There are certain important things to remember when taking the tablets.
  • Do not double the dose if you forget to take one of your pills.
  • Keep the pills in their original packaging at room temperature. They should be stored away from heat and direct sunlight.
  • Keep them safe and out of the reach of children.
  • Get a new prescription before the one you have runs out, and keep track of holidays, when pharmacies may be closed.
  • Return the remaining pills to the hospital if the treatment is discontinued.


You may experience some of the side effects mentioned here, though it is rare for a patient to have all of them. If you are taking other drugs, you may have certain side effects that are not listed here.

Always inform your doctor or nurse of the side effects you experience. They can prescribe drugs to help control them and can also give you advice on managing side effects. Do not stop taking tamoxifen without talking to your doctor first.


These are common and tend to be mild, though they can vary. Hot flashes and sweating can subside after the first few months. Some people continue having them throughout the time they are taking tamoxifen. It can help to lower your intake of nicotine, alcohol, and hot beverages containing caffeine such as tea and coffee. Dress in layers so you can remove clothing if you need to. Natural fabrics such as cotton may be most comfortable.

Tell your doctor if your hot flashes become bothersome. Low doses of certain antidepressants can help reduce hot flashes. The antidepressant paroxetine (Seroxat®) and fluoxetine (Prozac®) can make tamoxifen less effective, which is why doctors don't often prescribe them.


These may include discharge, itchiness, and dryness. Non-hormonal creams and gels or lubricants can help reduce vaginal dryness and discomfort during sex.


If you are still getting your period, these may become irregular, lighter, or stop altogether.


Nausea normally improves after a few weeks. Try to take your pills with food or at night. Tell your doctor or nurse if you have nausea or indigestion. They can advise you and drugs to help.


Tamoxifen can cause cataracts or other problems, though this is uncommon. If you have blurriness of vision or notice any changes in your vision, always contact your doctor or nurse.


Let your doctor or nurse know if you have headaches. Normally, this can be easily controlled with over-the-counter drugs.


Tamoxifen may cause dizziness. Tell your doctor or nurse if this is a problem.


Walking can stretch the muscle out and help with this. Tell your doctor if the leg cramps become a problem.


When you start to take tamoxifen, you may feel tired, drowsy, or feel like you have no energy. Try to pace yourself until this improves. It is important to strike the correct balance between getting enough rest and staying physically active. Taking short walks regularly will help you feel less tired. If you feel drowsy, don't drive or operate heavy machinery.


You may develop a mild rash. Let your doctor or nurse know if this happens. It is very important that you contact your doctor immediately if you develop a sever rash.


Your hair may become thinner when taking tamoxifen. This is normally mild. Your hair may thicken when you stop taking the drug.


You may gain weight when taking hormone therapy. Eating healthy meals and becoming more physically active can help you maintain a healthy weight. Your nurse can give you further advice on this.


You may have a lower sex drive when taking tamoxifen. When taking tamoxifen, men sometimes find that the treatment causes them sexual difficulties. Talk to your doctor or nurse for advice.


Some people go through mood swings or feel low or depressed while they are taking tamoxifen. Or it may be harder to think clearly or concentrate. Tell your doctor or nurse if this is a problem, especially if you are feeling depressed.


BLOOD CLOTS (Thrombosis)

Tamoxifen may slightly increase your chances of having a blood clot. Tell your doctor if you have a history of blood clots or deep vein thrombosis (DVT).

A blood clot may cause symptoms such as pain, reddening or swelling in a leg, difficulty breathing, and pain in the chest. Get in touch with your doctor immediately if you have any of these symptoms.

A blood clot is a serious matter, but your doctor can use drugs to thin your blood. Your doctor or nurse specialist can give you more information.


If you have been prescribed tamoxifen for cancer that has spread to your bone, you may have bone pain when you start taking the drug. Tumor flare can cause an increased level of calcium in the blood (hypercalcemia). The symptoms of this are nausea, vomiting, thirstiness, constipation, or sometimes a feeling of disorientation. If you have any of these symptoms, tell your doctor or nurse so they can give you treatment.


Some people who take tamoxifen have reported that the drug affects their ability to sing. If this is a worry of yours, talk to your cancer specialist.


Women who have gone through menopause and have taken tamoxifen for a long period of time are at a higher risk of developing uterine cancer. But this risk is offset by the benefits of taking tamoxifen. When uterine cancer is detected in time, the treatment is very successful. Abnormal vaginal bleeding may be an early sign, so if this happens it is very important that you let your specialist physician or nurse know so they can examine this. Bleeding is often caused by a non-cancerous condition, but always talk to your doctor or nurse.


Tamoxifen can change the way the liver functions. It is very unlikely you will notice any problems, though your doctor will take periodic blood samples to check whether your liver is working properly.


Taking tamoxifen after menopause may help prevent and reduce the risk of bone thinning. But taking it before menopause may cause some thinning of the bones. Taking regular walks will help you maintain strong bones. Eating a healthy diet, not smoking, and following guidelines for drinking alcohol will also help. Tell your doctor if you have any bone problems.



Your doctor will advise you not to become pregnant when taking tamoxifen. This is because tamoxifen can harm developing babies. It is important to use an effective, non-hormonal contraceptive during treatment and for a few months after the treatment has finished. Even if your periods have stopped or are irregular, you still have to use a contraceptive. You can talk to your doctor or nurse about this.


Women who have not gone through menopause yet may become pregnant when they have finished their tamoxifen treatment. Doctors normally recommend waiting for a few months after treatment with tamoxifen before trying to become pregnant. Talk to your doctor if you are trying to have children.


The side effects can be controlled or managed most of the time. However, they may be more problematic for some women. If this is the case, make sure you talk to your cancer doctor or nurse. They can normally suggest ways to improve the side effects. If things do not get better, go back to your oncologist or nurse. They may suggest trying something else.

It is very important that you do not stop taking tamoxifen without telling your doctor, as this may affect the success of the treatment. It the side effects are very bothersome and are unmanageable, your oncologist may suggest you start on a different hormone therapy.


Tamoxifen can interact with other drugs. For example, it can increase the effect of an anticoagulant called warfarin. Tell your doctor immediately if you are taking warfarin or other drugs. Some other drugs may make tamoxifen less effective.

Tell your doctor if you are taking any drugs, including complementary therapies, and herbal remedies.


If you have to go to the hospital for whatever reason other than cancer, always tell the doctors and nurses that you are taking tamoxifen. Explain that you are taking hormone therapy that no one should start or stop without taking to your cancer specialist in the first place.

Always let your dentist know that you are taking tamoxifen.