In the journals: Some antidepressants interfere with tamoxifen more than others

Tamoxifen (Nolvadex) is a selective estrogen receptor modulator, or SERM. It's commonly prescribed after surgery for early-stage estrogen receptor–positive breast cancer — that is, breast cancer that's fueled by estrogen. By blocking estrogen's activity in breast cells, tamoxifen reduces the risk of recurrence as much as 50%. For women at high risk, it reduces the likelihood of developing a first breast cancer by the same amount.

Unfortunately, not all women taking tamoxifen get its full benefit. Tamoxifen is converted in the body to its active form, endoxifen, by a member of the P450 family of enzymes called CYP2D6. Some women have a mutation in the gene that synthesizes CYP2D6 and may not metabolize tamoxifen as effectively as women with a normal gene.

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