Depression medicines make tamoxifen less effective-Study

The study warns that tamoxifen taken with popular antidepressants like Eli Lilly & Co.’s Prozac, Pfizer Inc.’s Zoloft and GlaxoSmithKline Plc’s Paxil can increase the risk of breast cancer recurrence.

Researchers from the aforementioned two institutes presented their findings Saturday at a meeting of the American Society of Clinical Oncology in Orlando.

What the study found

In their study, the research team found that using a combination of depression medicines and cancer prevention drug can virtually wipe out the benefit tamoxifen provides.

Tamoxifen is an estrogen suppressor which helps lower the risk that breast cancer will return and improves survival rates. The drug that cuts in half the chances of a breast cancer recurrence is consumed by nearly 500,000 women in the United States.

The novel study now shows that antidepressants like Paxil, Prozac and Zoloft, which are considered moderate-to-potent CYP2D6 inhibitors, interfere with the active ingredient in tamoxifen, which can double a woman's risk of having her cancer return.

"We've known that these CYP2D6 inhibitor drugs block the activation of tamoxifen chemically, but this is the first time there's evidence that these drugs are putting women at a much higher risk for recurrent breast cancer," said Robert Epstein, Medco's chief medical officer and one of the study authors.

How the research was conducted

To reach their findings, Epstein and colleagues studied about 1,300 women who were newly prescribed tamoxifen to treat breast cancer between 2003 and 2005. The team monitored the women for at least two years.

The research investigators assigned 353 women to take strong CYP2D6 inhibitor drugs such as Paxil, Prozac or Zoloft along with the tamoxifen, and 945 women to use tamoxifen only.

After comparing the two groups, the researchers found that women taking a combo of the CYP2D6 inhibitors and tamoxifen were 13.9% more likely to have their breast cancer tumors back compared to 7.5% of those taking just tamoxifen.

But the authors of the novel study have suggested that only certain antidepressants interfere with tamoxifen, so women should consult their doctors about which ones are safest.

About Breast Cancer

Brest cancer, caused by the development of malignant cells in the breast, is the second most common tumor in women, after skin tumors. According to the Atlanta-based U.S. Centers for Disease Control and Prevention estimates, about 187,000 women were diagnosed with breast cancer and 41,000 women died from the disease in 2005 (the most recent year for which CDC data are available).