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What is Tamoxifen?

Mary McMahon
Updated May 17, 2024
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Tamoxifen is a drug developed in the 1960s and used in treatment for certain types of breast cancers in both early and advanced stages. It is sold under a several trade names, including Nolvadex®, Valodex®, and Istubal®. In addition to being utilized in breast cancer treatment, tamoxifen is also used to treat some other health conditions, including infertility, bipolar disorder, and gynecomastia, a condition in which men develop breast tissue. This drug is only available by prescription, and it is taken orally, in a dosage determined by the prescribing doctor.

When a breast cancer is estrogen receptor positive, also known as hormone sensitive, tamoxifen can be used to treat the cancer. The drug acts as a block, inhibiting the growth of the cancer. The drug is usually taken in combination with other treatments, and people may take it for several years to prevent recurrence of the breast cancer at the original site, and to discourage the cancer from appearing in the other breast. The drug also reduces the risk of osteoporosis, a somewhat unexpected side effect.

Certain people who are at very high risk for breast cancer may take tamoxifen as a preventative, although this use is not widespread. The drug appears to become less effective over time, meaning that it could be useless in future treatment if someone has been taking it as a preventative, and it also has some serious side effects which should be carefully weighed before people embark on preventative use of tamoxifen.

On the low end of the scale, tamoxifen can cause nausea, hair loss, vomiting, bone pain, and weight gain. More seriously, it can contribute to the formation of blood clots and cataracts. The drug has also been linked with endometrial changes, and it has actually been classified as a carcinogen, because women who take tamoxifen are at increased risk of gynecological cancers, specifically uterine cancer. Tamoxifen usage can also cause birth defects if women use the drug while they are pregnant.

Despite the side effects, many doctors feel that taking tamoxifen is worth the risks. Other drugs which work in similar ways are also available, with tamoxifen being among the oldest of such drugs on the market. Before taking tamoxifen, patients should discuss their options with their doctors, and it may be a good idea to seek a second opinion from a breast cancer specialist to confirm the most appropriate and effective choice of treatment.

WiseGeek is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a WiseGeek researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Discussion Comments
By jennythelib — On Aug 25, 2011

@kat919 - My mom's half-sister did the same thing. The family actually tried to talk her out of it at first, because we thought it was just too radical. But my mom's best friend is going through breast cancer treatments right now, and so now she understands better what her sister wants to avoid.

My aunt is actually quite thrilled with the result. She had reconstructive surgery. See, she'd been quite large-breasted and had had three kids, so holding up "the girls" was quite a task. Her implants are just B size and, frankly, have a life that a woman in her teens could envy!

By Kat919 — On Aug 24, 2011

My grandmother and her sister both died of breast cancer in their fifties. My mom pursued genetic testing, and it turns out she has the gene, too.

The options available were not good. She actually tried tamoxifen for a while, but it made her quite sick.

That, I think, is what really drove the decision she ultimately made. Of course, she knew that with frequent mammograms, etc. there was a good chance that if she developed breast cancer, it would be caught quite early. And treatment today is much better than it was when her mom got sick.

But taking that tamoxifen made her realize that surviving isn't all there is to it; she doesn't want to get that sick. So she decided to have a double mastectomy. There's not zero chance now that she will get breast cancer, but it's very low.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

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