How Enclomiphene Affects LH

Clomiphene citrate is a racemic mixture of two isomers: enclomiphene (trans-isomer, approximately 60%) and zuclomiphene (cis-isomer, approximately 40%). Enclomiphene is the pharmacologically active component responsible for SERM activity at the pituitary. It competitively antagonizes estrogen receptors at hypothalamic and pituitary cells, blocking estradiol's inhibitory signal on GnRH release. The resulting increase in GnRH pulsatility drives increased LH secretion from anterior pituitary gonadotrophs. Critically, enclomiphene lacks the hepatic estrogenic agonism of zuclomiphene, meaning it does not raise SHBG or cause vision disturbances associated with retinal zuclomiphene accumulation. Its short half-life (approximately 10-12 hours) also means it clears rapidly, unlike zuclomiphene, which has a half-life of approximately 30 days and accumulates with repeated dosing.

At 12.5 mg/day, enclomiphene raises LH by 50-80% from baseline within 2-4 weeks in secondary hypogonadal men. At 25 mg/day, LH typically rises into the upper normal or mildly supranormal range (6-12 IU/L). The LH elevation is sustained throughout therapy and returns to baseline within 1-2 weeks of cessation. Unlike clomiphene, there is no prolonged zuclomiphene-mediated LH effect after stopping, making the pharmacokinetic profile cleaner and more predictable.

Check LH at baseline, then at 4-6 weeks into therapy to confirm response. If LH does not rise above 2 IU/L by 4-6 weeks at 25 mg/day, consider whether residual exogenous androgens are still suppressing the axis (started therapy too early) or whether primary pituitary pathology exists. For fertility protocols, LH response at 6 weeks should be confirmed with a concurrent semen analysis at 3 months. Post-therapy: recheck LH at 4-6 weeks after stopping to confirm sustainable axis function.

Enclomiphene 12.5-25 mg/day is the standard dose range. Start at 12.5 mg/day and uptitrate to 25 mg/day if LH response is insufficient at 6 weeks. Do not exceed 25 mg/day; there is no evidence that higher doses provide greater LH stimulation, and the risk of estradiol-related side effects increases. Unlike clomiphene, SHBG does not rise meaningfully with enclomiphene, so free testosterone tracks total testosterone accurately and does not require the same correction calculations needed during clomiphene therapy.