Tamoxifen and Antidepressants Combo Increase Risk of Breast Cancer Return

Results of a new study show that some popular antidepressants, like Zoloft, Paxil and Prozac, can negate the effectiveness of the breast cancer drug tamoxifen, substantially increasing the risk that the tumors may return.

A tamoxifen study by Medco Health Solutions, which was presented Saturday at a meeting of the American Society of Clinical Oncology, found that a certain class of antidepressants known as selective serotonin reuptake inhibitors (SSRIs), negate much of the effectiveness of tamoxifen, doubling the chance that the breast cancer will return when compared to women taking tamoxifen alone.

Researchers looked at 1,300 women taking tamoxifen to treat breast cancer. Those patients who were taking tamoxifen and antidepressant SSRI drugs together had a 14 percent chance of tumors recurring, while those taking tamoxifen alone had only a 7.5 percent chance. The study found that Paxil, Zoloft and Prozac had the highest increased breast cancer risk, at 16 percent.

While doctors and researchers have long suspected a connection between SSRIs and decreased effectiveness of tamoxifen, this study is the first large-scale study to confirm the risk.

About half a million women take tamoxifen in the United States, and the study raises serious concerns that a large percentage may be negating its effectiveness unknowingly. Nearly 30% of breast cancer survivors taking tamoxifen use some form of antidepressant to treat hot flashes, which are a side effect of tamoxifen.

SSRIs are part of a larger group of drugs called CYP2D6 inhibitors. Weaker CYP2D6 inhibitors, like Luvox and Lexapro, did not raise the recurrence risk for breast cancer patients. However, the study found that 60 percent of the women taking a CYP2D6 were using an SSRI.

Medco researchers say that physicians must be warned about the negative side effects of antidepressant SSRIs combined with tamoxifen. While the link has been studied for some time, many physicians are still unaware of the risk.