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Your guide to tamoxifen for breast cancer treatment

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This daily medication can help fight breast cancer — or stop you from getting it in the first place. Here’s who it’s for, how it works and the potential side effects.
Written by Emily Shiffer
Updated on August 23, 2022

Battling breast cancer can come with a multitude of treatments and medications. One of them is tamoxifen (Nolvadex®, Soltamox®). It’s a hormone therapy medication for hormone receptor-positive breast cancers. That means it targets breast cancers that need estrogen to grow. But it can also help keep certain people from developing breast cancer.

There are some risk factors for breast cancer that we can’t do anything about. Age is one. Family history is another. Women with close relatives who’ve had breast cancer are at a higher risk of getting it themselves. For people at high risk, taking tamoxifen has been shown to reduce the risk of getting breast cancer by up to 50%. That’s according to a review published in Hereditary Cancer in Clinical Practice.

When deciding how to manage or prevent breast cancer, it helps to have all the facts. Here is what you need to know about tamoxifen — plus, the potential side effects to be aware of.

(No matter what medication you’re taking, it’s important to make sure you’re not overpaying. Use the Optum Perks prescription discount card at the pharmacy to see how much you could save.)

How does tamoxifen work?

Tamoxifen is a selective estrogen receptor modulator, says Heather Thompson Mackey, DNP. She’s a nurse practitioner and senior director of cancer prevention and early detection at the Prevent Cancer Foundation. Tamoxifen blocks estrogen receptors in breast cancer cells. That starves the cancer cells of the hormone they need to multiply and grow, says Mackey.

Millions of people have used tamoxifen to prevent or treat breast cancer. It was first approved by the U.S. Food and Drug Administration in 1998 and has been well studied ever since.

Plus, it’s “approved for use in both pre- and post-menopausal women,” adds Mackey. That’s important because nearly 75% of post-menopausal breast cancers are hormone positive.

How do you take tamoxifen?

Tamoxifen is taken by mouth, either as a pill (Nolvadex®) or a liquid (Soltamox®). Typically, it’s taken once daily for 5 years. But some people may take it for up to 10 years.

Recommended reading: How to always remember to take your medication.

What are the benefits of tamoxifen?

The biggest benefit is that it can lower the risk of getting breast cancer. And it reduces the risk of it coming back.

A study was done on tamoxifen use in premenopausal women who had early-stage breast cancer. It found that when given for 5 years, tamoxifen lowered women’s chances of getting breast cancer again by about 40%. And it reduced their risk of death by nearly 30%.

What are the side effects of tamoxifen?

Woman holding pill bottle with two pills in her hand

Unfortunately, tamoxifen can also come with side effects. They tend to appear within the first few weeks of taking it.

“Most women tolerate tamoxifen very well,” says Mackey. “Some may have nausea when they first start taking it. But it seems to improve over time.”

She adds that within the first few weeks, the most common side effects include:

  • Hot flashes
  • Night sweats
  • Lowered sex drive
  • Abnormal menstrual cycles (in those who are premenopausal)
  • Vaginal dryness

“These may or may not improve over time,” adds Mackey. So talk to your doctor about other treatments or tweaks to daily habits that can help.

As with all medications, there is also a risk of more serious side effects. These include an increased risk of:

  • Blood clots
  • Liver problems
  • Stroke
  • Uterine cancer
  • Cataracts

These side effects are relatively rare for most women. For example, blood clots and uterine cancer happen in less than 1% of those taking tamoxifen.

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Who shouldn’t take tamoxifen?

Tamoxifen isn’t right for everyone. Here are some reasons that it might not be a good fit for you:

  • You’re at risk for blood clots. “If you have a history of blood clots or you take blood-thinning medication, you should not take tamoxifen,” says Mackey.
  • You’re at risk for heart issues. If you have a history of heart attacks or strokes, talk with your health care provider. Tamoxifen could increase the risk of another cardiovascular event.
  • You’re taking oral contraceptives. Women who take oral contraceptives should not take tamoxifen. “If you’re pregnant, trying to get pregnant or nursing, do not take tamoxifen. It could put your developing child at risk,” says Mackey.
  • You’re on certain antidepressants. Women who take CYP2D6 inhibitors should talk to their doctor before using tamoxifen. Examples include bupropion (Wellbutrin®), paroxetine (Paxil®) and fluoxetine (Prozac®). These can reduce the benefits of tamoxifen, says Mackey.
  • You have a history of uterine cancer. Tamoxifen can increase the chances of uterine cancer. So it’s not a good fit for those with a history of the disease.

Tamoxifen is excellent at preventing and treating breast cancer. But it’s important to weigh the pros and cons with your health care team. And don’t forget to use Optum Perks to get the best price on prescription medication. It’s easy — and free. Here’s how it works.

Additional sources
Tamoxifen to reduce breast cancer risk: Hereditary Cancer in Clinical Practice (2017). “Motivators and barriers of tamoxifen use as risk-reducing medication amongst women at increased breast cancer risk: a systematic literature review”
Statistics on hormone-positive breast cancer: Cleveland Clinic
Breast cancer recurrence study: Clinical Advances in Hematology and Oncology (2015). “Adjuvant endocrine therapy in premenopausal women with breast cancer”