Tamoxifen can reduce the risk of a breast cancer recurrence, but many women complain of side effects like hot flashes and weight gain.

Amanda MacMillan
October 26, 2017

In this week’s issue of People, former Victoria’s Secret model Jill Goodacre opens up about her five-year battle with breast cancer and the medication she’s been on to keep the disease at bay. Goodacre, who’s married to singer and actor Harry Connick Jr., went through surgery and radiation in 2012 after a tumor was detected via sonogram, and has taken the drug tamoxifen ever since.

As she approaches her five-year cancer-free mark, Goodacre says she’s looking forward to stopping tamoxifen. The medication can cause side effects, including weight gain, which Goodacre admits she’s struggled with.

“I’ve always been a pretty fit person, and so to be just rounder and heavier and not to really be able to do much about it—that’s been hard,” she told People. “It’s taken a lot out of my self-confidence.”

That’s a common problem among breast cancer survivors, says Nikita Shah, MD, medical director of the Cancer Risk Evaluation Program at Orlando Health UF Health Cancer Center. (Dr. Shah has not treated Goodacre, but does prescribe tamoxifen to many of her own patients.)

Still, tamoxifen can be lifesaving, says Dr. Shah, and for many women, its benefits outweigh its potential side effects. Here’s what else breast cancer patients and their loved ones should know about the pros and cons of this treatment.

It can be a treatment or a prevention

Tamoxifen is in a class of drugs known as selective estrogen receptor modulators, or SERMs. These drugs work by attaching to estrogen receptors in breast cells, blocking estrogen’s ability to cause cell mutations that lead to cancer.

The drug—taken as a pill or a liquid—is often prescribed to pre-menopausal women after surgery for early-stage breast cancer. Because surgeons can’t always be sure they removed all of the cancer cells, tamoxifen can reduce the risk that those leftover cells will continue to multiply and the cancer will return.

It can also be prescribed to women, pre- or post-menopause who have not been diagnosed with breast cancer, if they have a high risk (1.67% or higher) of developing it over the next five years. These women are usually 35 or older, and have risk factors such as a family history of cancer or a history of abnormal biopsies.

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It’s only effective for some types of cancer

Studies have shown that tamoxifen can reduce the risk of cancer in high-risk women by more than 30%. But because the drug affects estrogen receptors in the body, it only works against cancers that are estrogen-receptor-positive or progesterone-receptor positive. Together, these make up about two-thirds of all breast cancers, according to BreastCancer.org.

“The way tamoxifen works is you’re depriving your cancer cells of estrogen, which is their nutrition,” says Dr. Shah. “So that will only work for the cancers that are estrogen-fed or progesterone-fed.”

RELATED: 25 Breast Cancer Myths Busted

Other factors can affect how well it works, too

Some people have an abnormal version of an enzyme called CYP2D6, which may make tamoxifen less effective. (Some research has suggested this, although larger, more recent studies haven’t found a link.) Patients may want to consider being tested for this enzyme abnormality before starting tamoxifen, to make sure they’ll get the full benefit.

Certain medications, including diphenhydramine (Benadryl), cimetidine (Tagamet), and some antidepressants can also block the activity of the CYP2D6 enzyme. "That's why it's very important to make sure your oncologist knows every medication you're taking, including supplements," says Dr. Shah. 

Five years is recommended, but 10 years may be better

After breast cancer treatment, most women who take tamoxifen take it for five years. But recent studies have suggested that it can reduce women’s risk for breast cancer even further if it’s taken for 10 years, says Dr. Shah.

However, tamoxifen is only recommended after breast cancer treatment for women who haven’t gone through menopause yet; after menopause, other drugs—called aromatase inhibitors—are known to work better. “If a woman becomes post-menopausal during those five or 10 years she’s on tamoxifen, we will switch her to this other group of drugs that is 20 to 25% more effective,” says Dr. Shah.

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It does have side effects—but they may be overestimated

Despite its protective effects against cancer, some women stop taking tamoxifen because of side effects like hot flashes, mood swings, nausea, vomiting, or weight gain or loss. The drug can cause menstrual irregularities, and changes in sex drive or sleep patterns as well. (Tamoxifen also raises the risk for more serious health issues, like blood clots and uterine cancer; though for most women, the overall risk for these problems is still small.)

But many women who take tamoxifen are perimenopausal, and a recent study found that some women mistake naturally occurring symptoms of menopause with side effects of tamoxifen. In the study, symptom-related drop-out rates were similar across a nearly five-year period for women who took tamoxifen and for those who took a placebo pill.

“Patients will say I started taking tamoxifen and I gained 40 pounds,” says Dr. Shah. “But that’s probably a combination of hormonal and lifestyle changes they’re going through. Tamoxifen can cause some fluid retention, and it could maybe cause a 2- or 3-pound weight gain, but beyond that there are probably other things going on as well.”

Dr. Shah says it’s important to talk to your doctor if you’re experiencing side effects, rather than stopping a recommended course of tamoxifen. “There are ways to manage the side effects, and most of them are not permanent. They get better with time,” she says.