Generic name: tamoxifen [ ta-MOX-i-fen ]
Brand name: Soltamox
Dosage forms: oral solution (10 mg/5 mL), oral tablet (10 mg; 20 mg)
Drug classes: Hormones / antineoplastics, Selective estrogen receptor modulators

Medically reviewed by Sophia Entringer, PharmD. Last updated on Jul 29, 2024.

What is tamoxifen?

Tamoxifen blocks the actions of estrogen, a female hormone. Certain types of breast cancer require estrogen to grow.

Tamoxifen is used to treat some types of breast cancer in men and women.

Tamoxifen is also used to lower a woman's chance of developing breast cancer if she has a high risk (such as a family history of breast cancer).

Warnings

Taking tamoxifen may increase your risk of uterine cancer, liver cancer, stroke, or a blood clot in the lung, which can be fatal.

Do not use tamoxifen if you are pregnant. It could harm the unborn baby. Use a barrier form of birth control (such as a condom or diaphragm with spermicide) while you are using this medication and for at least 2 months after your treatment ends. You should not use tamoxifen if you are allergic to it, if you have a history of blood clots in your veins or your lungs, or if you are taking a blood thinner such as warfarin (Coumadin).

Before using this medicine, tell your doctor if you have liver disease, high triglycerides (a type of fat in the blood), a history of cataract, or a history of stroke or blood clot. Also tell your doctor if you if you are receiving chemotherapy or radiation treatment.

If you are taking tamoxifen to reduce your risk of breast cancer, you may need to take your first dose while you are having a menstrual period. You may also need to have a pregnancy test before you start taking this medicine, to make sure you are not pregnant. Follow your doctor's instructions.

To make sure this medication is not causing harmful effects, your doctor may want you to have mammograms and to perform routine breast self-exams on a regular basis. Your liver function may also need to be tested. Visit your doctor regularly.

Before taking this medicine

You should not use tamoxifen if you are allergic to it.

Tamoxifen may harm an unborn baby. You may need a pregnancy test to make sure you are not pregnant. Use birth control while using tamoxifen and for at least 2 months after your last dose. Tell your doctor if you become pregnant.

To prevent pregnancy while using tamoxifen, use a barrier form of birth control: condom, diaphragm, cervical cap, or contraceptive sponge. Avoid using hormonal birth control, including birth control pills, injections, implants, skin patches, and vaginal rings.

You should not use tamoxifen to reduce your risk of breast cancer if you also take warfarin (Coumadin, Jantoven).

To make sure tamoxifen is safe for you, tell your doctor if you have:

• a stroke or blood clot;

• liver disease;

• high cholesterol or triglycerides (a type of fat in the blood);

• cataracts;

• chemotherapy; or

• if you also use anastrozole or letrozole.

Taking tamoxifen may increase your risk of uterine cancer, liver cancer, stroke, or a blood clot in the lung, which can be fatal. Talk with your doctor about your own risks.

Do not breastfeed while using tamoxifen, and for at least 3 months after your last dose.

This medicine is not approved for use by anyone younger than 18 years old.

How should I take tamoxifen?

Take tamoxifen exactly as prescribed by your doctor. Follow all directions on your prescription label and read all medication guides or instruction sheets.

Measure liquid medicine with the supplied syringe or a dose-measuring device (not a kitchen spoon).

Take with or without food.

You may need to keep using this medicine for 5 to 10 years.

Have regular physical exams and mammograms, and self-examine your breasts for lumps on a monthly basis while using tamoxifen.

This medicine can affect the results of certain medical tests. Tell any doctor who treats you that you are using tamoxifen.

Store at room temperature away from moisture, heat, and light. Do not refrigerate or freeze. Throw away any leftover liquid medicine 3 months after you first opened the bottle.

What happens if I miss a dose?

Take the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take two doses at one time.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

What should I avoid while taking tamoxifen?

Follow your doctor's instructions about any restrictions on food, beverages, or activity.

Tamoxifen side effects

Get emergency medical help if you have signs of an allergic reaction to tamoxifen: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

Tamoxifen can increase your risk of stroke or blood clots. Call your doctor at once if you have:

• signs of a stroke - sudden numbness or weakness, severe headache, slurred speech, problems with vision or balance;

• signs of a blood clot in the lung - chest pain, sudden cough or shortness of breath, dizziness, coughing up blood; or

• signs of a blood clot deep in the body - pain, swelling, or warmth in one leg.

Also call your doctor at once if you have:

• unusual vaginal bleeding or discharge;

• blurred vision, eye pain or redness, seeing halos around lights;

• changes in your menstrual periods;

• pain or pressure in your pelvic area;

• a new breast lump;

• liver problems - nausea, upper stomach pain, itching, tired feeling, loss of appetite, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes); or

• high blood calcium - confusion, tiredness, nausea, vomiting, loss of appetite, constipation, increased thirst or urination, weight loss.

Common tamoxifen side effects may include:

• vaginal bleeding or discharge;

• hot flashes;

• swelling, weight gain;

• nausea; or

• mood changes.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Tamoxifen dosing information

Usual Adult Dose for Breast Cancer:

Metastatic breast cancer in women and men:
20 to 40 mg orally daily for 5 years; doses greater than 20 mg should be given in divided doses (morning and evening)

DCIS following breast surgery and radiation:
20 mg orally daily for 5 years

To reduce the incidence of breast cancer in women at high risk for breast cancer:
20 mg orally daily for 5 years

Comments:
-There are no data to support the use of this drug other than for 5 years.

Uses:
-Metastatic For metastatic breast cancer in women and men. In premenopausal women with metastatic breast cancer, this drug is an alternative to oophorectomy or ovarian irradiation. Patients whose tumors are estrogen receptor positive are more likely to benefit.
-Ductal Carcinoma in Situ (DCIS): In women with DCIS, following breast surgery and radiation, to reduce the risk of invasive breast cancer.
-Reduction in Breast Cancer Incidence in High Risk Women: To reduce the incidence of breast cancer in women at high risk. "High risk" is defined as women at least 35 years of age with a 5-year predicted risk of breast cancer greater than or equal to 1.67%, as calculated by the Gail Model.

Usual Adult Dose for Breast Cancer -- Adjuvant:

20 mg orally once daily or 10 mg orally 2 times daily
Duration of therapy: Up to 5 years

Comments:
-There are no data to support the use of this drug other than for 5 years.

Use: For the treatment of node-positive breast cancer in postmenopausal women following total mastectomy or segmental mastectomy, axillary dissection, and breast irradiation

Usual Pediatric Dose for McCune-Albright Syndrome:

Girls 2 to 10 years with McCune-Albright Syndrome and precocious puberty:
20 mg orally once daily
Duration of therapy: Up to 12 months

Use: McCune-Albright Syndrome; precocious puberty

Usual Pediatric Dose for Precocious Puberty:

Girls 2 to 10 years with McCune-Albright Syndrome and precocious puberty:
20 mg orally once daily
Duration of therapy: Up to 12 months

Use: McCune-Albright Syndrome; precocious puberty

Related/similar drugs

Verzenio, Trodelvy, estradiol, anastrozole, tamoxifen, letrozole, testosterone, Premarin, Arimidex

What other drugs will affect tamoxifen?

Many drugs can interact with tamoxifen, and some drugs should not be used at the same time. Tell your doctor about all other medicines you use. This includes prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible interactions are listed here.

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Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use tamoxifen only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

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