Tamoxifen (Nolvadex) and Fareston FAQs: Hormone Therapies to Prevent Breast Cancer Recurrence

Patient Expert

What is tamoxifen?

Tamoxifen (Nolvadex) is one of the most common drugs – perhaps THE most common drug – used as a part of the hormone therapy used to prevent breast cancer (either an initial diagnosis, or recurrence). Appropriate for women whose breast cancer is hormone-receptive, it’s most often prescribed to premenopausal women.

Tamoxifen has been on the market for nearly 35 years, and is considered the “gold standard” of hormone therapy for younger women. About 80 percent of women with breast cancer have a type that depends on female sex hormones – estrogen or progesterone – to grow. Tamoxifen prevents cancer cells from accessing those hormones, thus cancer growth is slowed and/or stopped.

How tamoxifen works.

Tamoxifen is a type of drug known as a SERM (selective estrogen-receptor modulator). It works by blocking estrogen from attaching itself to the special receptors on cancer cells.

Think of a crowded parking lot: while there are plenty of parking places, they’re all filled; so you’re forced to drive away. Tamoxifen “fills” a cell’s estrogen receptors, leaving no room for estrogen. Breast cancer cells deprived of estrogen go dormant, and almost always eventually die.

How effective is tamoxifen?

Unfortunately, there’s no cancer treatment that’s 100 percent guaranteed. How well tamoxifen will work for you and your cancer isn’t possible to predict. But statistically, tamoxifen has been shown to reduce the risk of breast cancer recurrence by about 50 percent. And when you’re talking a possible life-or-death situation, that’s pretty significant.

The typical treatment

The typical tamoxifen dosage is 20mg to 40mg daily, for women dealing with invasive breast cancer; and 20mg daily for women diagnosed with DCIS.

Studies have shown that women who don’t fill all of their tamoxifen prescriptions – those who aren’t diligent in taking it, once it’s prescribed – show an increased risk of recurrence. So make sure to take your pill every day, preferably at the same time.

Studies and clinical trials researching the optimal length of time to take tamoxifen are ongoing. Right now, the typical duration of treatment is 5 years.

Side effects

Thankfully, tamoxifen’s side effects are generally pretty mild. The following is a list of side effects you MAY encounter; of these, hot flashes, vaginal issues, and weight gain seem to be the most common.

•Hot flashes;

•Vaginal discharge, and/or dryness, and/or itching, and/or pain

•Fluid retention and/or weight gain

•Irregular periods



•Skin rash


•Increased fertility

In addition, there are possible serious side effects that are, thankfully, quite uncommon (under 1.5 percent of women taking tamoxifen are likely to encounter these):

•Increased blood clots

•Uterine or endometrial cancer



See more helpful articles:

Female Sex Hormones: What They Do and Why It Matters

Fear of Recurrence: Where Do You Stand?

A Guide to Breast Cancer Treatment

Tamoxifen: Does It Work For You?

Breast Cancer, Depression, and Tamoxifen: A Dangerous Trio

Tamoxifen: Personal Expereince and Research Differ in Side Effects

Breast cancer survivor and award-winning author PJ Hamel, a long-time contributor to the HealthCentral community, counsels women with breast cancer through the volunteer program at her local hospital. She founded and manages a large and active online survivor support network.