clomiphene — Selective Estrogen Receptor Modulator (SERM) — FDA-approved for ovulation induction; widely used off-label for male secondary hypogonadism
Clomiphene citrate is a racemic mixture of two geometric isomers: (1) Enclomiphene (trans-isomer, ~38%) — the active estrogenic antagonist at hypothalamic/pituitary ER; (2) Zuclomiphene (cis-isomer, ~62%) — predominantly estrogenic agonist with very long half-life (~30 days). Mechanism of action for male hypogonadism: Enclomiphene component blocks estrogen receptors at the hypothalamus → removes estradiol's negative feedback → pulsatile GnRH secretion increases → pituitary LH and FSH secretion increases → testicular testosterone production increases (endogenous). Unlike exogenous testosterone, clomiphene PRESERVES the HPG axis and maintains fertility (sperm production continues). Zuclomiphene accumulation: the long half-life cis-isomer accumulates with repeated dosing, has estrogenic agonist effects (not antagonist), and is responsible for visual side effects (blurred vision, photophobia, scotomata) and potential mood effects. This is why PURE enclomiphene (Androxal, without the zuclomiphene) has been developed — it offers the testosterone-raising benefit without zuclomiphene accumulation.
Overview
This page is part of Hormonaly's evidence-graded compound library. All clinical claims are linked to peer-reviewed sources via our dual-layer citation verification pipeline.
Compound Class
Selective Estrogen Receptor Modulator (SERM) — FDA-approved for ovulation induction; widely used off-label for male secondary hypogonadism
Mechanism of Action
Clomiphene citrate is a racemic mixture of two geometric isomers: (1) Enclomiphene (trans-isomer, ~38%) — the active estrogenic antagonist at hypothalamic/pituitary ER; (2) Zuclomiphene (cis-isomer, ~62%) — predominantly estrogenic agonist with very long half-life (~30 days). Mechanism of action for male hypogonadism: Enclomiphene component blocks estrogen receptors at the hypothalamus → removes estradiol's negative feedback → pulsatile GnRH secretion increases → pituitary LH and FSH secretion increases → testicular testosterone production increases (endogenous). Unlike exogenous testosterone, clomiphene PRESERVES the HPG axis and maintains fertility (sperm production continues). Zuclomiphene accumulation: the long half-life cis-isomer accumulates with repeated dosing, has estrogenic agonist effects (not antagonist), and is responsible for visual side effects (blurred vision, photophobia, scotomata) and potential mood effects. This is why PURE enclomiphene (Androxal, without the zuclomiphene) has been developed — it offers the testosterone-raising benefit without zuclomiphene accumulation.
Regulatory Status
FDA APPROVED for ovulation induction in women. All male use is OFF-LABEL. Inexpensive generic. No controlled substance scheduling.
Evidence Level
A — FDA-approved for ovulation induction (multiple RCTs). Off-label male use: Shabsigh 2005 (n=178, 25–50 mg/day, testosterone +168 ng/dL); Krzastek 2019 meta-analysis (9 studies, n=400+, consistent testosterone elevation with preserved fertility). Multiple observational studies support use in secondary hypogonadism. No Phase 3 RCT specifically for male hypogonadism (that's why 'off-label').