What is tamoxifen?

Tamoxifen (Nolvadex® or Soltamox®) is a drug that treats hormone receptor-positive (hormone-positive) breast cancer. It may also help prevent breast cancer. Since the Food and Drug Administration (FDA) approved tamoxifen in 1998, it has become one of the most widely used breast cancer treatments.

What is hormone receptor-positive breast cancer?

Breast cancer tumors that are hormone receptor-positive need the hormones estrogen or progesterone (or sometimes both) to grow. Approximately 75% of breast cancers are hormone-positive in post-menopausal patients. Your healthcare provider will perform a biopsy and laboratory testing to determine the cancer type and most effective treatment.

How does tamoxifen work?

Tamoxifen is a type of hormonal therapy known as a selective estrogen receptor modulator (SERM). The drug attaches to hormone receptors (specific proteins) in breast cancer cells. Once the medication is inside the cells, it stops the cancer from accessing the hormones they need to multiply and grow.

Who should use tamoxifen?

Tamoxifen can help women and men with hormone receptor-positive breast cancer. The drug can lower the risk of breast cancer in:

  • Women who are high-risk of breast cancer due to a family history of disease or mutated (changed) breast cancer (BRCA) genes.
  • Women and men who have already been diagnosed with breast cancer to prevent recurrence (return) of cancer, including:

Your doctor will determine if tamoxifen is right for you.

How effective is tamoxifen?

Millions of people have used tamoxifen to prevent or treat breast cancer. The drug may lower the risk of:

  • Breast cancer in the opposite breast by 50%.
  • Breast cancer recurrence in premenopausal women by 30% to 50%.
  • Breast cancer recurrence in postmenopausal women by 40% to 50%.
  • Initial breast cancer diagnosis by up to 40%.
  • Invasive breast cancer after the diagnosis of early-stage, noninvasive breast cancer (ductal carcinoma in situ or DCIS) by up to 50%.

What are the other benefits of taking tamoxifen?

In addition to lowering the risk of breast cancer and cancer recurrence, tamoxifen:

How do you take tamoxifen?

You must take tamoxifen daily by mouth, preferably at the same time each day. The drug comes in two forms:

  • Nolvadex® pill.
  • Soltamox® liquid.

How long should you take tamoxifen?

Most people take tamoxifen or other hormone therapy for at least five years and sometimes up to 10 years. Treatment length depends on the features of your cancer diagnosis.

Your healthcare provider may recommend taking tamoxifen for five years and then switching to different hormone therapy for several more years.

What are the side effects of taking tamoxifen?

Side effects of tamoxifen may include:

What are the risks of taking tamoxifen?

Rarely, tamoxifen may cause serious problems such as:

Is it safe to take tamoxifen during pregnancy?

Tamoxifen may cause birth defects. You shouldn’t take the medication if you’re pregnant or planning to become pregnant. To prevent pregnancy, talk to your healthcare provider about nonhormonal birth control options. (Hormonal contraceptives can fuel the growth of hormone-positive breast cancer). You’ll need to use contraception while taking tamoxifen and for two months after you stop the medication.

What other medications lower breast cancer risk?

Other medications that can reduce the risk of breast cancer include:

  • Raloxifene (Evista®) is another type of SERM that blocks estrogen receptors on breast cancer cells. Unlike tamoxifen, this drug is only approved for postmenopausal women and is not associated with increased risk of endometrial (uterine) cancer. It may lower the risk of invasive breast cancer by nearly 40%.
  • Aromatase inhibitors, including anastrozole (Arimidex®) and exemestane (Aromasin®), can lower estrogen levels in postmenopausal women.

When should I call the doctor?

You should call your healthcare provider if you’re taking tamoxifen and experience:

A note from Cleveland Clinic

Tamoxifen is a highly effective breast cancer treatment. It may significantly lower your risk of breast cancer recurrence or invasive breast cancer. People who are at high risk for breast cancer may take tamoxifen to reduce their chances of getting the disease. Your healthcare provider can discuss whether tamoxifen or another form of hormone therapy is right for you.

Last reviewed by a Cleveland Clinic medical professional on 10/24/2020.


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