Highlights for tamoxifen

  1. Tamoxifen oral tablet is only available as a generic drug. There is no brand-name version.
  2. Tamoxifen comes as an oral tablet and as an oral solution.
  3. Tamoxifen oral tablet is used to treat and help prevent breast cancer.

Important warnings

FDA warning: Serious side effects

  • This drug has a black box warning. This is the most serious warning from the Food and Drug Administration (FDA). A black box warning alerts doctors and patients about drug effects that may be dangerous.
  • Tamoxifen can increase the risk of serious and life-threatening events, including uterine cancer, blood clots, and stroke. These events can be fatal. You should discuss the potential benefits and risks of this drug with your doctor.

Other warnings

  • Cataracts warning: Tamoxifen can increase the risk of getting cataracts or needing cataract surgery. Tell your doctor if you have blurred vision. This may mean that you have cataracts and you may need surgery. Talk to your doctor about the risks and benefits of this drug.
  • Liver problems warning: This drug may increase your risk of liver problems. The signs of liver problems include loss of appetite and yellowing of your skin or the whites of your eyes. Tell your doctor if you have these symptoms. Talk to your doctor about the risks and benefits of this drug.
  • Blood thinners warning: If you’re taking a blood thinner medication, tamoxifen can increase the amount of the drug in your body. This may make it easier for you to bleed. If you have ductal carcinoma in situ (DCIS) or a history of blood clots and you must take a blood thinner, you shouldn’t use tamoxifen.
  • Call your doctor: You should contact your doctor right away if you have any of the following symptoms. Some of these symptoms may suggest that you’re experiencing a rare but serious side effect associated with tamoxifen:
    • new breast lumps
    • vaginal bleeding
    • changes in your menstrual cycle
    • changes in vaginal discharge
    • pelvic pain or pressure
    • swelling or tenderness in your calf
    • unexplained shortness of breath
    • sudden chest pain
    • coughing up blood
    • changes in your vision

What is tamoxifen?

Tamoxifen is a prescription drug. It comes as an oral tablet and an oral solution.

Tamoxifen oral tablet is only available as a generic drug. Generic drugs usually cost less than a brand-name drug.

Why it's used

Tamoxifen is used to treat and reduce the risk of certain types of breast cancer.

How it works

Tamoxifen belongs to a group of drugs called antiestrogens. A class of drugs is a group of medications that work in a similar way. These drugs are often used to treat similar conditions.

Antiestrogens work by blocking the effects of the hormone estrogen in the body. Estrogen may cause the growth of some types of breast tumors. Tamoxifen may block the growth of tumors that respond to estrogen.

Tamoxifen side effects

Tamoxifen oral tablet doesn’t cause drowsiness, but it can cause other side effects.

More common side effects

The more common side effects that occur with tamoxifen include:

  • hot flashes
  • vaginal discharge

If these effects are mild, they may go away within a few days or a couple of weeks. If they’re more severe or don’t go away, talk to your doctor or pharmacist.

Serious side effects

Call your doctor right away if you have serious side effects. Call 911 if your symptoms feel life-threatening or if you think you’re having a medical emergency. Serious side effects and their symptoms can include the following:

  • Changes in the lining (endometrium) of your uterus. These changes may mean serious problems are starting, including cancer of the uterus. Symptoms can include:
    • vaginal bleeding or bloody discharge in a rusty or brown color. You should call your doctor even if a small amount of bleeding occurs.
    • changes in your menstrual cycle, such as in the amount or timing of bleeding or increased clotting
    • pain or pressure in your pelvis (below your belly button)
  • Blood clots in your veins or lungs. These can occur for up to 2–3 months after you stop taking tamoxifen. Symptoms can include:
    • sudden chest pain
    • shortness of breath
    • coughing up blood
    • pain, tenderness, or swelling in one or both of your legs
  • Stroke. Symptoms can include:
    • sudden weakness, tingling, or numbness in your face, arm, or leg, especially on one side of your body
  • sudden:
    • confusion
    • trouble speaking
    • trouble seeing in one or both eyes
    • trouble walking
    • dizziness
    • loss of balance or coordination
    • severe headache with no known cause
  • Cataracts. Symptoms can include:
    • blurred vision
  • Liver problems. Symptoms can include:
    • loss of appetite
    • yellowing of your skin or the whites of your eyes (jaundice)

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs affect each person differently, we cannot guarantee that this information includes all possible side effects. This information is not a substitute for medical advice. Always discuss possible side effects with a healthcare provider who knows your medical history.

Tamoxifen may interact with other medications

Tamoxifen oral tablet can interact with other medications, vitamins, or herbs you may be taking. An interaction is when a substance changes the way a drug works. This can be harmful or prevent the drug from working well.

To help avoid interactions, your doctor should manage all of your medications carefully. Be sure to tell your doctor about all medications, vitamins, or herbs you’re taking. To find out how this drug might interact with something else you’re taking, talk to your doctor or pharmacist.

Examples of drugs that can cause interactions with tamoxifen are listed below.

Adrenal gland disorder drugs

Taking tamoxifen with certain medications for adrenal gland disorders can decrease the amount of tamoxifen in your blood. You shouldn’t use these drugs together. Examples of these drugs include:

  • aminoglutethimide

Blood thinners

Taking tamoxifen with a blood thinner can increase the amount of the blood thinner in your body. This may make it easier for you to bleed. If you must take a blood thinner and you have ductal carcinoma in situ (DCIS) or want to reduce your risk of breast cancer, you shouldn’t use tamoxifen.

Examples of blood thinners include:

  • warfarin

Bromocriptine

Taking tamoxifen with bromocriptine increases the amount of tamoxifen in your body. If you need to take these drugs together, your doctor may adjust your dosage of tamoxifen.

Cancer-fighting drugs

Taking tamoxifen with certain cancer drugs decreases the amount of the cancer drugs in your body. This means they won’t work as well. Taking tamoxifen with these drugs also increases your risk of blood clots. You should not use tamoxifen with these drugs.

Examples of these cancer drugs include:

  • letrozole
  • anastrozole

Taking tamoxifen with other cancer-fighting drugs increases your risk of blood clots. Examples of these drugs include:

  • doxorubicin
  • daunorubicin
  • vincristine
  • vinblastine
  • cyclophosphamide
  • cisplatin

Seizure drugs

Taking tamoxifen with certain seizure drugs may lower the amount of tamoxifen in your body. If you need to take these drugs together, your doctor may adjust your dosage of tamoxifen. Examples of these drugs include:

  • phenobarbital
  • fosphenytoin
  • phenytoin

Tuberculosis drugs

Taking tamoxifen with certain tuberculosis drugs can decrease the amount of tamoxifen in your body. If you need to take these drugs together, your doctor may increase your tamoxifen dosage. Examples of these drugs include:

  • rifampin
  • rifabutin
  • rifapentine

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs interact differently in each person, we cannot guarantee that this information includes all possible interactions. This information is not a substitute for medical advice. Always speak with your healthcare provider about possible interactions with all prescription drugs, vitamins, herbs and supplements, and over-the-counter drugs that you are taking.

Tamoxifen warnings

This drug comes with several warnings.

Allergy warning

Tamoxifen can cause a severe allergic reaction. Symptoms include:

  • trouble breathing
  • swelling of your throat or tongue
  • hives

Call 911 or go to the nearest emergency room if you develop these symptoms.

Don’t take this drug again if you’ve ever had an allergic reaction to it. Taking it again could be fatal (cause death).

Warnings for people with certain health conditions

For people with changes in the lining of the uterus: Tamoxifen can further increase your risk for changes in the lining of the uterus. If you have a history of this condition, talk to your doctor before using this drug. Let your doctor know if you develop menstrual changes, abnormal vaginal bleeding, changes in vaginal discharge, or pelvic pain or pressure. Your doctor may adjust your dosage or have you stop taking tamoxifen.

For people with a history of blood clots: Tamoxifen can further increase your risk of blood clots. If you have a history of this condition, talk to your doctor before using this drug. If you develop leg pain or swelling, shortness of breath, cough, or chest pain, tell your doctor and go to the emergency room right away.

For people with a history of stroke: Tamoxifen can further increase your risk of stroke. If you have a history of this condition, talk to your doctor before using this drug.

For people with a history of eye problems: Tamoxifen can further increase your risk of eye problems, such as cataracts. If you have a history of vision problems, talk to your doctor before using this drug. Let your doctor know if you have any changes in vision. They may lower your dosage or have you stop taking the drug.

For people with liver problems: Tamoxifen can further increase your risk of liver problems. If you have a history of this condition, talk to your doctor before using this drug. If you develop signs of liver damage, such as yellowing of your skin or the whites of your eyes, tell your doctor. They may adjust your dosage of this medication.

Warnings for other groups

For pregnant women: Tamoxifen is a category D pregnancy drug. That means two things:

  1. Research in humans has shown adverse effects to the fetus when the mother takes the drug.
  2. This drug should only be used during pregnancy in serious cases where it's needed to treat a dangerous condition in the mother.

Talk to your doctor if you’re pregnant or planning to become pregnant. Ask your doctor to tell you about the specific harm that may be done to the pregnancy. This drug should only be used if the potential risk to the pregnancy is acceptable given the drug’s potential benefit.

For women who are breastfeeding: It isn’t known if tamoxifen passes into breast milk. If it does, it may cause side effects in a child who is breastfed. Talk to your doctor if you breastfeed your child. You may need to decide whether to stop breastfeeding or stop taking this medication.

For seniors: Older adults may process drugs more slowly. This can cause the drug to build up in your body, which may increase your risk of side effects.

For children: This drug shouldn’t be used in people under the age of 18 years.

How to take tamoxifen

All possible dosages and forms may not be included here. Your dose, form, and how often you take it will depend on:

  • your age
  • the condition being treated
  • how severe your condition is
  • other medical conditions you have
  • how you react to the first dose

Dosage for metastatic breast cancer

Generic: Tamoxifen

  • Form: oral tablet
  • Strengths: 10 mg, 20 mg

Adult dosage (ages 18 years and older)

The typical recommended dosage is 20–40 mg per day taken in one or divided doses for 5 years. If you take more than 20 mg per day, you should take half of your dose in the morning and half of your dose in the evening.

Child dosage (ages 0–17 years)

A safe and effective dosage in people under the age of 18 years hasn’t been determined.

Dosage for adjuvant treatment of breast cancer

Generic: Tamoxifen

  • Form: oral tablet
  • Strengths: 10 mg

Adult dosage (ages 18 years and older)

The typical recommended dosage is 20–40 mg per day taken in one or divided doses for 5 years. If you take more than 20 mg per day, you should take half of your dose in the morning and half of your dose in the evening.

Child dosage (ages 0–17 years)

A safe and effective dose in people under the age of 18 years hasn’t been determined.

Dosage for ductal carcinoma in situ (DCIS)

Generic: Tamoxifen

  • Form: oral tablet
  • Strengths: 10 mg

Adult dosage (ages 18 years and older)

The typical recommended dosage is 20 mg taken once per day.

Child dosage (ages 0–17 years)

A safe and effective dosage in people under the age of 18 years hasn’t been determined.

Dosage for reduction in breast cancer incidence in high-risk women

Generic: Tamoxifen

  • Form: oral tablet
  • Strengths: 10 mg

Adult dosage (ages 18 years and older)

The typical recommended dosage is 20 mg taken once per day.

Child dosage (ages 0–17 years)

A safe and effective dosage in people under the age of 18 years hasn’t been determined.

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs affect each person differently, we cannot guarantee that this list includes all possible dosages. This information is not a substitute for medical advice. Always speak with your doctor or pharmacist about dosages that are right for you.

Take as directed

Tamoxifen is used for long-term treatment. It has shown to be most effective if it’s used for 5 years. It comes with serious risks if you don’t take it as prescribed.

If you don’t take it at all: Not taking tamoxifen could affect your treatment outcome. If there’s a reason that you don’t want to take your medication, talk to your doctor.

If you take too much: Taking too much tamoxifen may cause the following symptoms:

  • shaky hands
  • dizziness
  • unsteady walk
  • changes in heart rhythm (QT prolongation)

What to do if you miss a dose: If you forget to take your dose, take it as soon as you remember. If it’s just a few hours before the time for your next dose, take only one dose at that time.

Never try to catch up by taking two doses at once. This could result in dangerous side effects.

How to tell if the drug is working:

  • For breast cancer treatment: Your doctor will do blood tests and imaging studies periodically to check the progress of your cancer treatment. Your doctor will tell you if the drug is working to treat your cancer.
  • For cancer prevention: Your doctor may do tests and exams to check for cancer.

Important considerations for taking tamoxifen

Keep these considerations in mind if your doctor prescribes tamoxifen for you.

General

  • You can take your tamoxifen with or without food.
  • You can cut or crush the tablet.

Storage

  • Store tamoxifen at room temperature between 68°F and 77°F (20°C and 25°C).
  • Don’t freeze tamoxifen.
  • Keep it away from light and high temperature.
  • Don’t store this medication in moist or damp areas, such as bathrooms.

Refills

A prescription for this medication is refillable. You should not need a new prescription for this medication to be refilled. Your doctor will write the number of refills authorized on your prescription.

Travel

When traveling with your medication:

  • Always carry your medication with you. When flying, never put it into a checked bag. Keep it in your carry-on bag.
  • Don’t worry about airport X-ray machines. They can’t hurt your medication.
  • You may need to show airport staff the pharmacy label for your medication. Always carry the original prescription-labeled box with you.
  • Don’t put this medication in your car’s glove compartment or leave it in the car. Be sure to avoid doing this when the weather is very hot or very cold.

Clinical monitoring

Your doctor may do tests to make sure that your treatment is going well. They may check your:

  • blood cell counts, including for red blood cells, white blood cells, and platelets
  • liver function

Are there any alternatives?

There are other drugs available to treat your condition. Some may be more suitable for you than others. Talk to your doctor about possible alternatives.

Disclaimer: Healthline has made every effort to make certain that all information is factually correct, comprehensive, and up-to-date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or other healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.