On Antidepressants and Tamoxifen? Listen Up!

If you're one of the women who have somehow been able to escape the night sweats and hot flashes that are typically associated with the hormonal treatment tamoxifen, please know that you may not been getting the full, intended benefit from this specific hormonal therapy.

For years, hundreds of thousands of women have been taking tamoxifen because the drug reduces our risk of getting breast cancer again or of getting it in the first place. The downside of this, of course, is that tamoxifen is a hormonal therapy, which means that it's also subjecting those same hundreds of thousands of women to some pretty rough menopausal side effects, like hot flashes and night sweats.

Tamoxifen, Prozac, and the enzyme CYP2D6

Interestingly, though, a certain small percentage of women taking tamoxifen have always been immune from the drug's malevolent side effects, and we've always considered them the lucky ones. Recently, however, researchers found out why these women haven't had to deal with tamoxifen's unpleasant features--and it turns out that their "good fortune" maybe wasn't so good at all.  

In short, the scientists have discovered an enzyme in the body called CYP2D6 that controls the metabolism of drugs like tamoxifen. That is, CYP2D6 actually breaks down tamoxifen into a usable form that can be absorbed by our bodies to battle stray cancer cells or prevent new ones from developing. Which is great. But the bad news is that that CYP2D6 also controls the metabolism of some other drugs--namely, the class of antidepressants that includes Prozac and Paxil.

Some antidepressants hog all the CYP2D6

Next, the research revealed that most women not suffering from tamoxifen's side effects happened to also be taking Prozac and Paxil. This means that, after CYP2D6 gets through breaking down these particular antidepressant drugs, there's not enough of the enzyme left over to also turn the tamoxifen into a usable cancer-cell hunter. And since the human body can't absorb unmetabolized tamoxifen, the women taking antidepressants like Prozac and Paxil have probably not been getting the degree of protection that hormonal therapy is supposed to offer.

So what to do? If you are on tamoxifen and taking an antidepressant, see your doctor soon. You might need to switch to another antidepressant, such as Lexapro or Effexor, which doesn't keep CYP2D6 from making tamoxifen available to your body.