Clomiphene citrate is a selective estrogen receptor modulator (SERM) developed for ovulation induction in women. Off-label use in men leverages its HPG-axis effects.
Mechanism — Blocks estrogen receptors at the hypothalamus, which normally provide negative feedback. The brain perceives low estrogen, increases GnRH, which drives LH and FSH, which drive testosterone and sperm production.
Use case — Secondary hypogonadism in younger men who want to preserve fertility. Typical 12.5-25 mg/day or every other day. Useful for post-TRT axis restart.
Caveats — Mood side effects (especially the zuclomiphene isomer) — visual disturbances, emotional lability. Enclomiphene (the trans isomer) is the cleaner option but harder to source. Doesn't work for primary hypogonadism (testicular failure).