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Tamoxifen, Oral ta-MOKS-ih-fen

What are other names for this medicine?

Type of medicine: antiestrogen

Generic and brand names: tamoxifen, oral

What is this medicine used for?

This medicine is taken by mouth to treat:

  • treat breast cancer in men and women that has spread to other parts of the body (metastatic).
  • treat breast cancer in women who have already received early treatment with surgery, radiation, or chemotherapy to lower the chance of a spreading (metastatic) cancer or new breast cancer.
  • lower the chance of getting a more serious (spreading) type of breast cancer in women who have already received surgery and radiation for ductal carcinoma in situ (DCIS; a type of cancer that is only in the milk ducts).
  • lower the chance of getting breast cancer in women with a higher than normal chance of getting breast cancer in the next 5 years (high-risk), due to their age, medical history, and family history.

It may be used for other conditions as determined by your healthcare provider.

What should my healthcare provider know before I take this medicine?

Before taking this medicine, tell your healthcare provider if you have ever had:

  • an allergic reaction to any medicine
  • a stroke
  • blood clots
  • high cholesterol

Tell your healthcare provider if you are scheduled for major surgery or have recently had a long period of bed rest after a broken bone in a cast. This may increase your chance of blood clots.

Do not take this medicine if you are taking medicine that reduces the chance of blood clots forming such as warfarin (Coumadin).

Females of childbearing age: Do not take this medicine if you are pregnant or breast-feeding because it can harm the baby. Talk to your healthcare provider if you need birth control. Birth control pills may not prevent pregnancy while you are taking this medicine. Do not become pregnant during treatment with this medicine or for 2 months after you stop taking this medicine. If you become pregnant, contact your healthcare provider right away. Do not breast-feed while you are receiving this medicine.

How do I take it?

Read the Medication Guide that comes in the medicine package when you start taking this medicine and each time you get a refill.

Check the label on the medicine for directions about your specific dose. Take this medicine exactly as your healthcare provider prescribes. You may take it with or without food. Do not stop taking it, even if you feel better. You may have to take this medicine for a long time, sometimes for as long as 5 years.

What if I miss a dose?

If you miss a dose, use it as soon as you remember unless it is almost time for the next scheduled dose. In that case, skip the missed dose and use the next one as directed. Do not use double doses. If you are not sure of what to do if you miss a dose, or if you miss more than one dose, contact your healthcare provider.

What if I overdose?

If you or anyone else has intentionally taken too much of this medicine, call 911 or go to the emergency room right away. If you pass out, have seizures, weakness or confusion, or have trouble breathing, call 911. If you think that you or anyone else may have taken too much of this medicine, call the poison control center. Do this even if there are no signs of discomfort or poisoning. The poison control center number is 800-222-1222.

Symptoms of an acute overdose may include: unusual muscle movements, twitching, loss of balance, dizziness, irregular heartbeat, seizures.

What should I watch out for?

This medicine may increase your risk for cancer of the uterus, cataracts, strokes, liver problems, and blood clots in the legs or lungs. Contact your healthcare provider immediately if you notice abnormal vaginal bleeding, irregular or abnormal menstrual periods, groin pain or pressure, chest pain, pain or swelling in your legs, trouble breathing, changes in vision, yellowing of skin or eyes, or weakness on one side of your body.

Your healthcare provider will see you regularly while you are taking this medicine. You will need to have regular blood tests to see how this medicine affects you. Keep all appointments for these tests.

You need to have regular eye exams while on this medicine because it may cause cataracts.

This medicine may cause dizziness. Do not drive or operate machinery unless you are fully alert.

If you need emergency care, surgery, or dental work, tell the healthcare provider or dentist you are taking this medicine.

What are the possible side effects?

Along with its needed effects, your medicine may cause some unwanted side effects. Some side effects may be very serious. Some side effects may go away as your body adjusts to the medicine. Tell your healthcare provider if you have any side effects that continue or get worse.

Life-threatening (Report these to your healthcare provider right away. If you cannot reach your healthcare provider right away, get emergency medical care or call 911 for help): Allergic reaction (hives; itching; rash; trouble breathing; tightness in your chest; swelling of your lips, tongue, and throat).

Serious (report these to your healthcare provider right away): Abnormal vaginal itching, bleeding, or discharge; unusual weakness or tiredness; bone pain; pain or swelling in your legs; shortness of breath; vision changes; menstrual changes; sudden weakness on one side of your body; sudden trouble walking or loss of balance; sudden or severe headache; chest pain; coughing blood; confusion; weight gain; unusual bleeding or bruising; yellowing of your skin or eyes.

Other: Dizziness, hot flashes, hoarseness, mild headache, nausea, vomiting, loss of appetite, loss of taste for food (tell your healthcare provider if it is severe), change in sexual desire or ability, mood changes, constipation, diarrhea, swelling in hands or feet, hair thinning.

What products might interact with this medicine?

When you take this medicine with other medicines, it can change the way this or any of the other medicines work. Nonprescription medicines, vitamins, natural remedies, and certain foods may also interact. Using these products together might cause harmful side effects. Talk to your healthcare provider if you are taking:

  • aminoglutethimide (Cytadren)
  • antidepressants such as fluoxetine (Prozac) and paroxetine (Paxil)
  • bromocriptine (Parlodel)
  • cancer medicines such as aldesleukin (Proleukin), anastrozole (Arimidex), cyclophosphamide (Cytoxan), and letrozole (Femara)
  • estrogens such as Premarin, estradiol (Estrace) and birth control pills, patches, vaginal rings, and shots (talk to your healthcare provider if you need birth control)
  • medicine that reduces the chance of blood clots forming such as warfarin (Coumadin)
  • medroxyprogesterone (Depo-Provera)
  • natural remedies such as black cohosh, chasteberry, dong quai, melatonin, soy isoflavones, or St. John's wort
  • phenobarbital
  • rifampin (Rifadin, Rimactane) and rifabutin (Mycobutin)

Do not eat grapefruit or drink grapefruit juice while taking this medicine. Grapefruit affects the way this medicine works and may increase the risk of side effects.

If you are not sure if your medicines might interact, ask your pharmacist or healthcare provider. Keep a list of all your medicines with you. List all the prescription medicines, nonprescription medicines, supplements, natural remedies, and vitamins that you take. Be sure that you tell all healthcare providers who treat you about all the products you are taking.

How should I store this medicine?

Store this medicine at room temperature. Keep the container tightly closed. Protect it from heat, high humidity, and bright light.


This advisory includes selected information only and may not include all side effects of this medicine or interactions with other medicines. Ask your healthcare provider or pharmacist for more information or if you have any questions.

Ask your pharmacist for the best way to dispose of outdated medicine or medicine you have not used. Do not throw medicine in the trash.

Keep all medicines out of the reach of children.

Do not share medicines with other people.


Developed by RelayHealth.
Medication Advisor 2012.1 published by RelayHealth.
Last modified: 2010-12-02
Last reviewed: 2010-12-02
This content is reviewed periodically and is subject to change as new health information becomes available. The information is intended to inform and educate and is not a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional.
© 2012 RelayHealth and/or its affiliates. All rights reserved.
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