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Interview: David A. Flockhart, MD, PhD
Indiana University School of Medicine
Division of Clinical Pharmacology

I’m talking with Indiana University School of Medicine pharmacologist Dr. David Flockhart about a new study showing that some antidepressants can raise the risk for the return of breast cancer in patients on the anti-cancer drug tamoxifen.

• The central fact is that women who’ve had breast cancer and are on both tamoxifen and some popular antidepressants—Paxil, Prozac, Zoloft—are more than twice as likely to see their cancer return compared to women not taking both drugs.

• The study, in which Lockhart has been centrally involved, looked at 1300 women. Those on both drugs had a cancer recurrence rate of 16% compared to a rate of 7.5% for women not on both drugs. The problem has something to do with how some antidepressants interfere with the functioning of an enzyme that apparently is necessary for tamoxifen to work at full strength.

• Not all antidepressants interfere with tamoxifen; Celexa, Lexapro and Luvox, for example, were not implicated in high cancer recurrence rates.

• Tamoxifen came into its own in 1998 when a large study showed that it helped prevent the return of breast cancer. As of 2004 it’s been the world’s best-selling breast cancer treatment drug. It works by starving breast cancer cells of the estrogen they need to grow and develop. Half a million women in the U.S. take tamoxifen and 30% of them are also on antidepressants.

• It’s taken 10 years for Flockhart and other researchers to gather enough evidence to convince the FDA to issue a warning to doctors. The Administration plans to add a warning to tamoxifen’s label.

Additional Resources:

• Find out more about Dr. David Flockhart
• Learn more about tamoxifen and antidepressants

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