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Home > Understanding Breast Cancer > Risk Factors and Prevention > Risk-Lowering Drugs


Risk-Lowering Drugs



Research Fast Facts: Prevention
Fact Sheet

Chemoprevention is a term used to describe the use of drugs to lower the risk of breast cancer in women at higher risk. Tamoxifen and raloxifene are the only two drugs FDA-approved for breast cancer chemoprevention.  

Please note, these drugs are not chemotherapy drugs. Tamoxifen is a hormone therapy drug used for both breast cancer treatment and prevention. Raloxifene is only used in the prevention setting and not for breast cancer treatment.  

Both tamoxifen and raloxifene are taken in pill form.  


For a summary of research studies on tamoxifen and raloxifene and breast cancer prevention, visit the Breast Cancer Research section.

Tamoxifen and raloxifene


Fact Sheet

Breast cancer risk

Both tamoxifen and raloxifene can lower the risk of [151]:

Tamoxifen and raloxifene only reduce the risk of estrogen receptor-positive breast cancers. Neither drug reduces the risk of estrogen receptor-negative cancers [151].  

Tamoxifen is more effective than raloxifene in lowering breast cancer risk. However, raloxifene has fewer harmful side effects than tamoxifen (see table below) [151]. This makes raloxifene a better choice for some women.

Side effects

Tamoxifen and raloxifene have some long-term side effects (see table below) and may not be suitable for all women at higher risk. For example, tamoxifen increases the risk of cataracts and cancer of the uterus [151]. Talk to your health care provider about the potential harms and benefits of these drugs.   

Learn more about talking to your health care provider.  

Summary of the differences between tamoxifen and raloxifene




Who can take the drug? 

Premenopausal (ages 35 and older) and postmenopausal women

Postmenopausal women only

What are common short-term side effects?  

  • Hot flashes
  • Vaginal discharge
  • Vaginal dryness or itching
  • Irregular periods or spotting (uterine bleeding)  

Other side effects are less common.

  • Hot flashes
  • Leg cramps

What are the possible health risks? 

  • Cancer of the uterus or endometrium (lining of the uterus)
  • Cataracts
  • Blood clots in the large veins (deep venous thrombosis)
  • Blood clots in the lungs (pulmonary emboli)
  • Stroke

These effects occur mainly in older postmenopausal women.

  • Blood clots in the large veins (deep venous thrombosis)
  • Blood clots in the lungs (pulmonary emboli)
  • Stroke

These effects occur mainly in older postmenopausal women.

What about use in breast cancer treatment? 

Effective in the treatment of hormone receptor-positive breast cancer.

Has not been shown to be effective for the treatment of breast cancer.

Adapted from selected sources [151,263-270].


Komen Perspectives 

Read our perspective on risk-lowering drugs (March 2012).* 


Tamoxifen and anti-depressants

Certain types of anti-depressants called selective serotonin reuptake inhibitors (SSRIs) can interfere with the metabolism of tamoxifen (how tamoxifen works in the body) [150,271]. If you are taking SSRIs to treat depression or menopausal symptoms, talk to your health care provider about possible drug interactions and other options for treating symptoms.

BRCA1/2 gene mutations and tamoxifen

Researchers are assessing whether tamoxifen lowers the risk of breast cancer in women who have a BRCA1 or BRCA2 gene mutation [248,272-273]. Some studies have suggested that tamoxifen may be more effective in preventing breast cancer in BRCA2 carriers than BRCA1 carriers [273-275]. BRCA2-related tumors are more likely to be estrogen receptor-positive [274]. Tamoxifen works by attaching to estrogen receptors and only reduces the risk of estrogen receptor-positive cancers.  

Some findings have shown tamoxifen might offer benefit to BRCA1/2 carriers who have been diagnosed with breast cancer in the past [115,272,275]. The risk of breast cancer in the unaffected (opposite) breast may be reduced by as much as 75 percent with two to four years of tamoxifen use [272].

Ethnicity and tamoxifen

Although we know much about the potential benefits and harms of tamoxifen for white women, at this time, there are few data for women of other ethnicities. However, African American women may get less benefit and more harm from tamoxifen than white women. African American women have a lower rate of breast cancer than white women and are more likely to suffer some of the harmful health effects of tamoxifen [276-277].

Aromatase inhibitors

Aromatase inhibitors are hormone drugs that are part of standard treatment for estrogen receptor-positive breast cancer in postmenopausal women (learn more). There are three aromatase inhibitors that are FDA-approved for the treatment of breast cancer in the U.S.: anastrozole (Arimidex), letrozole (Femara), and exemestane (Aromasin). They appear to be equally effective in treating breast cancer.  

These drugs are now being studied to see whether they may lower breast cancer risk in postmenopausal women at high risk.

Exemestane (Aromasin) and anastrozole (Arimidex)

Findings from randomized controlled trials of cancer-free postmenopausal women at high risk have shown that the aromatase inhibitors exemestane (Aromasin) and anastrozole (Arimidex) may lower the risk of breast cancer by about half [152,525].

Unlike tamoxifen and raloxifene, exemestane and anastrozole do not appear to increase the risk of blood clots [152,525]. However, exemestane, anastrozole and other aromatase inhibitors can cause menopausal symptoms, a loss of bone density and other side effects (learn more) [278-281].  

The American Society for Clinical Oncology (ASCO) and the National Comprehensive Cancer Network (NCCN) now recommend exemestane as a risk-lowering drug option for postmenopausal women at higher risk of breast cancer. (These recommendations were made before the findings on anastrozole were published.) However, exemestane and anastrozole do not yet have FDA-approval for use in the chemoprevention setting. These drugs are only FDA-approved for use in breast cancer treatment.

Learn about exemestane, anastrozole and breast cancer treatment.

Learn about the side effects of aromatase inhibitors.  

Other aromatase inhibitors

The aromatase inhibitor drug letrozole is also being studied to see whether it may lower risk in postmenopausal women at high risk of breast cancer.  

Learn about aromatase inhibitors and breast cancer treatment.

Other risk-lowering drugs

Other drugs currently used to treat breast cancer are under study for use in prevention and new risk-lowering drugs are being developed.  

If you are at higher risk of breast cancer and are considering joining a clinical trial of risk-lowering drugs, discuss the potential risks and benefits with your health care provider.  

Learn more about emerging areas in chemoprevention.

Learn more about clinical trials

Prescription drug assistance

Medicare and many insurance providers offer prescription drug plans. One may already be included in your policy or you may be able to buy an extra plan for prescriptions. And, you may qualify for assistance from programs that help with drug costs or offer low-cost or free prescriptions.  

Tamoxifen is available in a generic form (cheaper than the name brand).  

Starting September 24, 2014, the Affordable Care Act will require new insurance plans to cover the cost (with no co-payments) of tamoxifen and raloxifene for women at high risk of breast cancer. Learn more about this coverage and the Affordable Care Act. Read Komen’s statement applauding the government’s decision to cover these risk-lowering drugs.

Learn more about insurance plans and prescription drug assistance programs.  


Komen Support Resources  

  • Our breast care helpline 1-877 GO KOMEN (1-877-465-6636) provides free, professional support services and help finding local support groups. Our trained and caring staff are available to you and your family Monday through Friday from 9:00 a.m. to 10:00 p.m. EST and from 6:00 a.m. to 7:00 p.m. PST. 
  • Our Message Boards offer online forums to share your thoughts or feelings about subjects related to breast cancer. Our Women at Higher Risk of Breast Cancer forum within the Message Boards offers women at higher risk a place to share their own unique experiences and challenges.


*Please note, the information provided within Komen Perspectives articles is only current as of the date of posting. Therefore, some information may be out of date at this time.   

Updated 01/21/14 


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Inherited Gene Mutations  next 
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