An antidepressant commonly prescribed for women undergoing breast cancer treatment has been shown to promote the development and growth of breast tumors in women.
Researchers at the City of Hope cancer research center screened 446 drugs in wide circulation to identify how they disrupt the balance of sex hormones in humans and influence the development and progress of diseases like breast cancer. They found that paroxetine — better known by its commercial name Paxil — has a weak estrogenic effect that could promote the development and growth of breast tumors in women.
Paxil was being taken by about a quarter of the depressed cancer patients in City of Hope’s study. Researchers found that Paxil behaves as endocrine-disrupting chemical that blocks the production of a liver enzyme needed to metabolize tamoxifen. Tamoxifen is the usual anti-estrogen therapy for certain breast cancers in premenopausal women and the standard treatment for breast cancer in postmenopausal women.
A 2010 study found that breast cancer patients in Canada taking Paxil were more likely to die of breast cancer than those taking other antidepressants when they were also taking tamoxifen.
Last summer, the Food and Drug Administration approved the marketing of a low dose of paroxetine as nonhormonal treatment for hot flashes and other symptoms of menopause. The new version of paroxetine is being marketed as Brisdelle.