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Tamoxifen and Raloxifene to Lower Breast Cancer Risk
T?amoxifen and raloxifene have been shown to reduce the risk of breast cancer in women with a higher-than-average risk. But these drugs have risks and side effects to consider before taking them.
What kind of medications are tamoxifen and raloxifene?
Tamoxifen and raloxifene are the only drugs approved in the US to help lower the risk of breast cancer. Although for some people, other drugs called aromatase inhibitors might also be an option.
Tamoxifen and raloxifene are selective estrogen receptor modulators (SERMs). This means that they block estrogen in some tissues of the body. And they act like estrogen in others.
Estrogen can fuel the growth of breast cancer cells. Both tamoxifen and raloxifene block estrogen in breast cells. This is why these medications can help lower breast cancer risk.
These medications are used more often for other reasons.
- Tamoxifen can be used as treatment for certain breast cancers, such as hormone receptor-positive breast cancer and advanced or recurrent endometrial and ovarian cancers.
- Raloxifene is used mostly to prevent and treat osteoporosis (very weak bones) in women who have gone through menopause.
When used to lower the risk of breast cancer, these medications are typically taken for 5 years. Both are pills that are taken once a day. Tamoxifen also comes in a liquid form.
Tamoxifen can be an option before or after menopause. But raloxifene is only approved for post-menopausal women.
To learn more about who these drugs may be right for, see Deciding Whether to Use Medicine to Reduce Breast Cancer Risk.
How much do these medications lower the risk of breast cancer?
The effect of these drugs on breast cancer risk has varied in different studies. When the results of all the studies are taken together, the overall reduction in risk of breast cancer is about 40%.
What would this mean for me?
Although a medication that cuts your risk by about 40% sounds like it must be a good thing, what it means for you depends on how high your risk is in the first place. This is called your baseline risk.
For example, if you had a 5% baseline risk of getting breast cancer in the next 5 years, you would be considered at increased risk. A 5% risk would mean that over the next 5 years, 5 of 100 women with your risk would be expected to get breast cancer. A 40% reduction in your risk would mean your risk goes down to 3%. This would be a 2% change overall.
The benefit of this treatment to you depends on your individual risk before any treatment. There are other things to consider as well, such as the risk of any side effects of the medication. Your doctor can estimate your breast cancer risk based on factors like your age, medical history, and family history. This can help you see how much benefit you might get from taking one of these medications.
Are there other benefits to taking these medications?
Both tamoxifen and raloxifene can help prevent osteoporosis, a severe weakening of the bones that can increase the risk of bone fractures. It is more common after menopause.
What are the main risks and side effects of taking these medications?
There are side effects to consider before taking SERM medications.
The most common side effects of these medications are symptoms of menopause. These include hot flashes and night sweats. Tamoxifen can also cause vaginal dryness and vaginal discharge.
Premenopausal women who take tamoxifen can have menstrual changes. Menstrual periods can become irregular or even stop. Although periods often start again after the medicine is stopped, they don’t always. Some women go into menopause. This is more likely if you are close to menopause when you start taking the medicine.
Both tamoxifen and raloxifene increase your risk of developing blood clots in a vein in your leg (deep venous thrombosis) or in your lungs (pulmonary embolism). These clots can sometimes cause serious problems, and even death. In the major studies of these drugs for breast cancer prevention, the risk of blood clots during 5 years of treatment was less than 1 in 100 women treated. This risk could be higher if you had a serious blood clot in the past. For this reason, these drugs are often not recommended to lower breast cancer risk for anyone with a history of blood clots.
Other serious blood clots, such as a blood clot in the brain that causes a stroke, have also been seen in people on tamoxifen. You might want to discuss this with your doctor, especially if you have a higher risk or history of a stroke or heart attack (a blood clot in the heart blood vessels). See Deciding Whether to Use Medicine to Reduce Breast Cancer Risk.
Because tamoxifen acts like estrogen in the uterus, it can increase your risk of cancers of the uterus. These include endometrial cancer and uterine sarcoma. It's also linked to a higher risk of endometrial pre-cancers. The increased risk seems to affect women over 50, but not younger women.
The overall increase in the risk of uterine cancer with tamoxifen use is low at less than 1%. The risk goes back to normal within a few years of stopping the medicine.
If you have had surgery to remove the uterus (hysterectomy), you are not at risk for endometrial cancer or uterine sarcoma. You do not have to worry about these cancers.
If you are taking tamoxifen, tell your doctor if you have any unusual vaginal bleeding or spotting, especially after menopause. These are possible symptoms of uterine cancer.
Raloxifene does not act like estrogen in the uterus and is not linked to an increased risk of uterine cancer.
Tamoxifen has been linked with an increased chance of developing cataracts, a clouding of the lens of the eye. This causes blurry vision.
Raloxifene does not have this side effect.
More resources
Learn more about using medicines to lower breast cancer risk.
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- References
Developed by the American Cancer Society medical and editorial content team with medical review and contribution by the American Society of Clinical Oncology (ASCO).
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Last Revised: March 30, 2026
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