Baby Tam (Low-Dose Tamoxifen)

Tamoxifen is commonly used to reduce the risk of invasive breast cancer or a recurrence of non-invasive disease if someone has been treated for DCIS, LCIS, or atypical ductal hyperplasia.

But because of potential serious risks, including blood clots, endometrial cancer, and stroke, as well as troubling side effects, like hot flashes, many people either don’t start the medicine or stop taking it early. Studies suggest that only about 4–10% of people prescribed tamoxifen after a non-invasive diagnosis take it for breast cancer prevention.

Many researchers and advocates wondered if a lower dose of tamoxifen — 5 mg per day instead of the regular 20 mg — could reduce breast cancer risk without the serious side effects. Many doctors refer to this lower dose as “baby tam.”

In 2023, long-term results from the TAM-01 study found that a 5-mg daily dose of tamoxifen reduced the risk of invasive breast cancer or a recurrence after non-invasive breast disease. This was the first study to show that baby tam could reduce breast cancer risk.

In 2026, a study that combined results from TAM-01 plus two other studies on baby tam found that compared to placebo, low-dose tamoxifen reduced the risk of invasive breast cancer after DCIS or other non-invasive disease. But the benefits depended on menopausal status. Among post-menopausal women, those taking baby tam had a 10-year absolute reduction in invasive breast cancer risk of 11.2%. This means if someone’s personal risk of developing invasive disease after DCIS was 20%, taking baby tam knocked that risk down to 8.8%. Among pre-menopausal women, there wasn’t any difference in risk reduction between women taking low-dose tamoxifen or women taking placebo, though there was a slight reduction in the risk of invasive breast cancer in the opposite breast.

Although the results of TAM-01 and other studies have found that baby tam reduces the risk of invasive breast cancer after non-invasive disease, the studies didn’t look at whether low-dose tamoxifen reduces breast cancer risk in people at high risk of the disease for other reasons, such as strong family history or a BRCA mutation. So doctors are hesitant to recommend baby tam for everyone at high risk.

Experts also have noted that the TAM-01 study found no difference in adherence between the two tamoxifen treatment groups. This means the same number of people taking the standard dose of tamoxifen completed the full course of treatment as people taking low-dose tamoxifen. So if a lower dose doesn’t mean more people stick to their treatment plans, the experts said people should take the standard dose because it has more research backing it and has been used longer.

The side effects of low-dose tamoxifen are similar to those caused by the standard dose: hot flashes, night sweats, vaginal discharge, and fatigue. But studies on baby tam found that low-dose tamoxifen caused fewer and less severe side effects than the standard dose.

In the TAM-01 study, women taking baby tam had one extra hot flash per day compared to women taking the placebo. Earlier studies show that taking the standard 20-mg dose of tamoxifen doubles the number of hot flashes per day.

Rates of blood clots were similar between women taking baby tam and women taking the placebo. This is much different from the three-fold increase in blood clot risk seen in studies using the standard dose of tamoxifen for breast cancer risk reduction. Similarly, rates of endometrial cancer were very low in both treatment groups — only one woman taking baby tam was diagnosed with stage I endometrial cancer. This is about five times lower than rates in studies using standard-dose tamoxifen.

If you’ve been diagnosed with non-invasive breast disease, like DCIS or LCIS, and your doctor recommends medicine to reduce your risk of invasive breast cancer, you may want to ask about low-dose tamoxifen.

If you’re at high risk for breast cancer for other reasons, it’s not clear if baby tam is as effective as the standard dose. But if you’re having severe side effects from the dose of tamoxifen you’re on, you can talk to your doctor about lowering the dose and discuss the risks and benefits of doing so.