The Who, What, Where, When and Sometimes, Why.


Tamoxifen (Nolvadex) has been used for over 40 years to treat hormone-receptor positive early, locally advanced and metastatic breast cancers. It’s used to treat breast cancer in both women and men.

Learn about tamoxifen and other hormone therapies (endocrine therapies) for metastatic breast cancer.

How does tamoxifen work?

Hormone receptor-positive breast cancers need estrogen (a female hormone) to grow.

Tamoxifen attaches to the estrogen receptors in the cancer cell, blocking estrogen from attaching to the receptors. This slows or stops the growth of the tumor by preventing the cancer cells from getting the hormones they need to grow.

Tamoxifen and treatment for early and locally advanced breast cancers

Tamoxifen lowers the risk of [89]:

  • Breast cancer recurrence (a return of breast cancer)
  • Breast cancer in the opposite breast
  • Death from breast cancer

Tamoxifen is a pill taken every day for 5-10 years. For premenopausal women, tamoxifen may be combined with ovarian suppression.

The benefits of tamoxifen may last 20 years after you stop taking it [98-100].

Learn about the importance of completing treatment with tamoxifen.

Find a list of questions on hormone therapy (endocrine therapy) you may want to ask your health care provider.


For a summary of research studies on tamoxifen for early breast cancer, visit the Breast Cancer Research Studies section.

Taking tamoxifen for more than 5 years

Findings from a large randomized clinical trial showed taking tamoxifen for 10 years reduced the risk of breast cancer recurrence and death more than taking tamoxifen for 5 years [101].

These findings have led to increased use of tamoxifen for more than 5 years, especially among premenopausal women who can’t take aromatase inhibitors and women with breast cancers at higher risk of recurrence.

Taking tamoxifen for a longer time means a continued risk of health effects, such as endometrial cancer (cancer of the lining of the uterus) [101]. For premenopausal women, tamoxifen may also impact fertility.

Discuss the benefits and risks of taking tamoxifen for more than 5 years with your health care provider.

Learn more about tamoxifen and fertility

Click on the topics below to learn more.

Tamoxifen can lower the risk of breast cancer in women who have a high risk of breast cancer (but have not been diagnosed) [102].

Learn more about risk-lowering drugs and other options for women at high risk of breast cancer

Side effects of tamoxifen include menopausal symptoms, such as hot flashes and vaginal dryness.

Before you begin taking tamoxifen, talk with your health care provider about possible side effects and how to manage them.

Learn more about the side effects of tamoxifen.

It’s important to follow the treatment plan (for medications and other therapies) prescribed by your health care provider in terms of:

  • Timing
  • Dose
  • Frequency

Breast cancer treatment is most effective when all parts of the treatment plan are followed as prescribed.

Completing tamoxifen therapy

To get the most benefit from tamoxifen, you need to take the full recommended course of treatment. People who complete the full course have better survival than those who don’t [95-97].

Tamoxifen for breast cancer treatment is prescribed for 5-10 years. The length of treatment along with side effects, such as menopausal symptoms, can make it tough to complete treatment. Talk with your health care provider about ways to ease these and other side effects.

If you have trouble remembering to take your medicine, a pillbox or setting an alarm on your watch or phone (you may be able to download an app) may help.

However, you don’t need to worry if you miss a day or two.

Learn more about the importance of following your breast cancer treatment plan.

Learn about ways to manage hot flashes and other menopausal symptoms.

Some types of antidepressants called selective serotonin reuptake inhibitors (SSRIs) can interfere with the metabolism of tamoxifen (how tamoxifen works in the body) [86].

Some SSRIs (such as fluoxetine (Prozac), paroxetine (Paxil) and sertraline (Zoloft)) may interfere with tamoxifen. However, it’s not known whether they might affect tamoxifen treatment for breast cancer.

Whether these SSRIs may impact the effectiveness of tamoxifen is under study.

If you’re taking an SSRI to treat depression or menopausal symptoms, talk with your health care provider about possible drug interactions and other treatment options.

Learn about ways to manage hot flashes and other menopausal symptoms.

In addition to treating breast cancer and lowering risk, tamoxifen may have other health benefits. It may [103-104]:

  • Improve blood cholesterol profile by lowering LDL levels (the “bad” cholesterol). A better cholesterol profile may lower the risk of heart disease.
  • Help maintain bone density and thus, lower the risk of osteoporosis and bone fractures in postmenopausal women.

Learn more about tamoxifen on the National Institutes of Health’s Medline Plus website

Susan G. Komen® Support Resources

  • Do you need help? We’re here for you. The Komen Patient Care Center is your trusted, go-to source for timely, accurate breast health and breast cancer information, services and resources. Our navigators offer free, personalized support to patients, caregivers and family members, including education, emotional support, financial assistance, help accessing care and more. Get connected to a Komen navigator by contacting the Breast Care Helpline at 1-877-465-6636 or email to get started. All calls are answered Monday through Thursday, 9 a.m to 7 p.m. ET and Friday, 9 a.m. to 6 p.m. ET. Se habla español.
  • The Komen Breast Cancer and Komen Metastatic (Stage IV) Breast Cancer Facebook groups are places where those with breast cancer and their family and friends can talk with others for friendship and support.
  • Our fact sheets, booklets and other education materials offer additional information.


Prescription drug assistance

Hormone therapy drug costs can quickly become a financial burden for you and your family.

Medicare and many insurance companies offer prescription drug plans. One may already be included in your policy, or you may be able to buy an extra plan for prescriptions.

Tamoxifen is a pill, so it’s covered under your health insurance plan’s prescription drug benefit rather than the plan’s medical benefit. This means there are usually out-of-pocket costs, which can add up over time.

You may qualify for programs that help with drug costs or offer low-cost or free prescriptions.

Generic drugs cost less than name brand drugs but are just as effective.

Many cancer centers have financial counselors who can discuss insurance and cost coverage with you.

Learn more about insurance plans and prescription drug assistance programs

Learn about other financial assistance programs.

Komen Financial Assistance Program

Susan G. Komen® created the Komen Financial Assistance Program to help those struggling with the costs of breast cancer treatment by providing financial assistance to eligible individuals.

To learn more about this program and other helpful resources, call the Komen Breast Care Helpline at 1-877 GO KOMEN (1-877-465-6636) or email

Se habla español.

Susan G. Komen®‘s position on fairness in oral cancer drug coverage

Insurance coverage of oral cancer drugs

Cancer medications given through an IV into a vein or by an injection (under the skin or into a muscle) are usually covered under a health insurance plan’s medical benefit. However, oral cancer drugs (cancer medications that are pills) are usually covered under a health insurance plan’s prescription drug benefit.

As a result, people often find themselves facing high out-of-pocket costs when filling prescriptions for oral cancer drugs. Sometimes these costs can be thousands of dollars a month.

The impact of high cost-sharing

High prescription drug costs and the resulting out-of-pocket burden on patients are a barrier to care. They can prevent people from getting the medications prescribed by their health care providers.

No one should be forced to get less appropriate treatment because an insurer gives more coverage for IV and injectable drugs than for pills.

Efforts to increase fairness in drug coverage

Komen supports state and federal efforts to require insurers to provide the same or better coverage for oral cancer drugs as they do for IV and injectable cancer drugs. This would help make sure patients have access to affordable, appropriate treatment.

Become a Komen Advocacy Insider

Sign up to be a Komen Advocacy Insider and get informed when action is needed on drug coverage issues at the state or national level.


 Updated 04/12/24



Fact Sheet


Questions to Ask Your Doctor

Hormone Therapy and Side Effects


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