Antidepressants Reduce the Effectiveness of Tamoxifen

Taking tamoxifen at the same time as certain drugs that treat depression and hot flashes may reduce the cancer drug’s ability to prevent breast cancer recurrence. The offenders in the study—Paxil (paroxetine), Prozac (fluoxetine), and Zoloft (sertraline)—are part of a class of drugs that inhibit CYP2D6, an enzyme that converts tamoxifen to its active form.

A U.S study found that after two years, 7.5 percent of women who took only tamoxifen had a recurrence, compared with 16 percent who took Paxil, Prozac, or Zoloft—drugs considered to be the most potent CYP2D6 inhibitors. That difference translates to a 120 percent increase in the risk of breast cancer recurrence. Patients taking the so-called weaker antidepressants, Celexa (citalopram), Lexapro (escitalopram), and Luvox (fluvoxamine), did not have an increased risk of recurrence.

However, a Dutch study presented at the meeting did not find that simultaneous use was unsafe, most likely because of the small number of patients in the study who took both drugs, said Julie Gralow, MD, of the Seattle Cancer Care Alliance, at a press briefing. (Gralow was not involved in either study.) The Dutch trial included less than half the number of patients in the U.S. study who took the drugs concurrently—150 versus 353 women. Other drugs to treat depression and hot flashes that do not inhibit CYP2D6 should be considered for tamoxifen patients, said Gralow.