Why is this medication prescribed?
Tamoxifen is used to treat breast cancer that has spread to other parts of the body in men and women. It is used to treat early breast cancer in women who have already been treated with surgery, radiation, and/or chemotherapy. It is used to reduce the risk of developing a more serious type of breast cancer in women who have had ductal carcinoma in situ (DCIS; a type of breast cancer that does not spread outside of the milk duct where it forms) and who have been treated with surgery and radiation. It is used to reduce the risk of breast cancer in women who are at high risk for the disease due to their age, personal medical history, and family medical history.
Tamoxifen is in a class of medications known as antiestrogens. It blocks the activity of estrogen (a female hormone) in the breast. This may stop the growth of some breast tumors that need estrogen to grow.
How should this medicine be used?
Tamoxifen comes as a tablet to take by mouth. Tamoxifen is usually taken once or twice a day with or without food. Take tamoxifen at around the same time(s) every day. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain anything you do not understand. Take tamoxifen exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.
Swallow tamoxifen tablets whole; do not split, chew, or crush them. Swallow the tablets with water or any other nonalcoholic drink.
If you are taking tamoxifen to prevent breast cancer, you will probably take it for five years. If you are taking tamoxifen to treat breast cancer, your doctor will decide how long your treatment will last. Do not stop taking tamoxifen without talking to your doctor.
If you forget to take a dose of tamoxifen, take the missed dose as soon as you remember it, and take your next dose as usual. However, if it is almost time for your next dose, skip the missed dose and continue your regular dosing schedule. Do not take a double dose to make up for a missed one.
Other uses for this medicine
Tamoxifen is also used sometimes to induce ovulation (egg production) in women who do not produce eggs but wish to become pregnant. Tamoxifen is also sometimes used to treat McCune-Albright syndrome (MAS; a condition that may cause bone disease, early sexual development, and dark colored spots on the skin in children). Talk to your doctor about the possible risks of using this drug for your condition.
This medication may be prescribed for other uses; ask your doctor or pharmacist for more information.
What special precautions should I follow?
Before taking tamoxifen,
- tell your doctor and pharmacist if you are allergic to tamoxifen or any other medications.
- tell your doctor and pharmacist what prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Be sure to mention any of the following: aminoglutethimide (Cytadren); anastrozole (Arimidex), bromocriptine (Parlodel); cancer chemotherapy medication such as cyclophosphamide (Cytoxan, Neosar) letrozole (Femara); medroxyprogesterone (Depo-Provera, Provera, in Prempro); phenobarbital; and rifampin (Rifadin, Rimactane). Your doctor may need to change the doses of your medications or monitor you carefully for side effects.
- in addition to the conditions listed in the IMPORTANT WARNING section, tell your doctor if you have or have ever had high blood levels of cholesterol.
- tell your doctor if you are pregnant or plan to become pregnant. You should not plan to become pregnant while taking tamoxifen or for 2 months after your treatment. Your doctor may perform a pregnancy test or tell you to begin your treatment during your menstrual period to be sure that you are not pregnant when you begin taking tamoxifen. You will need to use a reliable nonhormonal method of birth control to prevent pregnancy while you are taking tamoxifen and for 2 months after your treatment. Talk to your doctor about the types of birth control that are right for you, and continue to use birth control even if you do not have regular menstrual periods during your treatment. Stop taking tamoxifen and call your doctor right away if you think you have become pregnant during your treatment. Tamoxifen may harm the fetus.
- tell your doctor if you are breast-feeding. You should not breastfeed during your treatment with tamoxifen.
- tell all of your doctors and other health care providers that you are taking tamoxifen.
- you will still need to look for early signs of breast cancer since it is possible to develop breast cancer even during treatment with tamoxifen. Talk to your doctor about how often you should examine your breasts yourself, have a doctor examine your breasts, and have mammograms (x-ray examinations of the breasts). Call your doctor right away if you find a new lump in your breast.
What should I do if I forget a dose?
Take the missed dose as soon as you remember it. However, if it is almost time for the next dose, skip the missed dose and continue your regular dosing schedule. Do not take a double dose to make up for a missed one.
What side effects can this medication cause?
Tamoxifen may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:
- increased bone or tumor pain
- pain or reddening around the tumor site
- hot flashes
- excessive tiredness
- thinning of hair
- weight loss
- stomach cramps
- loss of sexual desire or ability (in men)
Some side effects can be serious. If you experience any of the following symptoms or those listed in the IMPORTANT WARNING section, call your doctor immediately:
- vision problems
- loss of appetite
- yellowing of the skin or eyes
- unusual bruising or bleeding
- swelling of the eyes, face, lips, tongue, throat, hands, arms, feet, ankles, or lower legs
- muscle weakness
Tamoxifen may increase the risk that you will develop other cancers, including liver cancer. Talk to your doctor about this risk.
Tamoxifen may increase the risk that you will develop cataracts (clouding of the lens in the eye) that may need to be treated with surgery. Talk to your doctor about this risk.
Tamoxifen may cause other side effects. Call your doctor if you have any unusual problems while taking this medication.
What should I know about storage and disposal of this medication?
Keep tamoxifen in the container it came in, tightly closed, and out of reach of children. Store it at room temperature and away from excess heat and moisture (not in the bathroom).
Unneeded medications should be disposed of in special ways to ensure that pets, children, and other people cannot consume them. However, you should not flush this medication down the toilet. Instead, the best way to dispose of your medication is through a medicine take-back program. Talk to your pharmacist or contact your local garbage/recycling department to learn about take-back programs in your community. See the FDA’s Safe Disposal of Medicines website (http://goo.gl/c4Rm4p) for more information if you do not have access to a take-back program.
It is important to keep all medication out of sight and reach of children as many containers (such as weekly pill minders and those for eye drops, creams, patches, and inhalers) are not child-resistant and young children can open them easily. To protect young children from poisoning, always lock safety caps and immediately place the medication in a safe location – one that is up and away and out of their sight and reach. http://www.upandaway.org
In case of emergency/overdose
In case of overdose, call the poison control helpline at 1-800-222-1222. Information is also available online at https://www.poisonhelp.org/help. If the victim has collapsed, had a seizure, has trouble breathing, or can’t be awakened, immediately call emergency services at 911.
Symptoms of overdose may include:
- uncontrollable shaking of a part of the body
What other information should I know?
- Keep all appointments with your doctor and the laboratory. Your doctor will order certain lab tests to check your body’s response to tamoxifen.
- Before having any laboratory test, tell your doctor and the laboratory personnel that you are taking tamoxifen.
- Do not let anyone else take your medication. Talk to your pharmacist if you have any questions about refilling your prescription.
It is important for you to keep a written list of all of the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.