Tamoxifen (Nolvadex): Is it REALLY Working for You?

Patient Expert

Thanks to fellow SharePoster Jolene Boyd, a startling issue involving tamoxifen was recently brought to light. Jolene's recent post on this site cited some studies showing that common antidepressant medications Prozac and Paxil might interfere with the way tamoxifen is metabolized. In plain English, if you're taking Paxil or Prozac at the same time you're taking tamoxifen, you may not be getting the benefit from tamoxifen that you should be.

Considering antidepressants are often prescribed for women suffering from tamoxifen-induced hot flashes or depression, this is something we should pay attention to. But how? Who among us can call up a tamoxifen/antidepressant expert and ask questions? That's one of the reasons why the site you're on right now, mybreastcancer.com, is so valuable. Site producer Sarah Park contacted science writer and site expert Lila de Tantillo, and Lila did the research and interviews that we, as laymen, really can't do. Her post on the Prozac/Paxil/tamoxifen interface is fascinating, and revelatory.

But wait, there's more. (Do I sound like the late-night television CD salesman?) After reading Jolene's initial post, I clicked on some of the links she cited. One of them was an interesting piece from the January 2007 Mayo Medical Laboratories newsletter, Communiqué. The article explained, in excruciating detail (unless you're a chemistry major, and then it would probably be fascinating), the science behind tamoxifen absorption. I understood it" barely. But after I'd struggled through the bulk of the article, I found at the end a table detailing other drugs that might interfere with tamoxifen. And that was VERY interesting.

Turns out it's not just Prozac or Paxil that might diminish tamoxifen's effectiveness. Wading through a long list of drugs listed by their scientific name, not brand name, I laboriously Googled each one to see what it might be. And guess what I found? Tagamet. And Zantac. Both very common heartburn relief remedies. Zoloft, another antidepressant also sometimes used to treat irritable bowel syndrome (IBS), or chronic indigestion of unknown cause. Wellbutrin, yet another antidepressant. Celebrex, taken by millions for arthritis. So if you're on tamoxifen, it's not just Paxil and Prozac about which you might want to question your oncologist.

In addition, the Mayo Lab article cites the fact that up to 10% of Caucasians (and 2% of African-Americans, and 1% of Asians) are naturally deficient in a certain enzyme that aids in metabolism of a number of drugs, including tamoxifen. If you happen to be in that group-and tests are currently being developed to test for that-then tamoxifen might not be effective for you. And what does "not effective" translate to? According to a long-term clinical study cited in the Mayo letter, women who either don't metabolize tamoxifen well naturally; or whose use of other drugs (like Paxil/Prozac) inhibit tamoxifen's effectiveness, were three times more likely to see a recurrence of their breast cancer.

So, how concerned should you be? If you've finished your course of tamoxifen, here's my advice: move on. You can't go back and alter how well it worked for you at this point. But if you're currently taking tamoxifen-especially if you're also taking another prescription drug that might affect how it works-you might want to mention this emerging information to your oncologist.