Tamoxifen Citrate

Also known as: tamoxifen, Nolvadex (branded), SERM

Hormone Restoration

In plain English

Tamoxifen blocks estrogen's effect in some tissues while acting like estrogen in others. It is FDA-approved to treat and prevent certain breast cancers. In men's hormone care it is sometimes used off-label to treat or prevent breast tissue growth (gynecomastia) or to raise testosterone. It is taken as a tablet.

The science

Tamoxifen is a selective estrogen receptor modulator that antagonizes estrogen receptors in breast tissue while acting as a partial agonist in bone and endometrium. It is FDA-approved for treatment and risk reduction of hormone-receptor-positive breast cancer; the NSABP P-1 prevention trial showed ~49% reduction in invasive breast cancer in high-risk women. In men, off-label uses include preventing/treating gynecomastia—a randomized dose-response study in men on antiandrogen therapy showed 20 mg/day markedly reduced breast events—and, like other SERMs, raising endogenous testosterone via increased gonadotropins. Notable risks are venous thromboembolism and (in women with a uterus) endometrial hyperplasia/cancer from its endometrial agonism. Compounded tamoxifen tablets/capsules for gynecomastia or testosterone support are off-label.

References

• Fisher et al., J Natl Cancer Inst 1998 (NSABP P-1 prevention trial)
• Randomised placebo-controlled dose-response trial, Eur Urol (tamoxifen prophylaxis for bicalutamide-induced gynaecomastia)