RESEARCH MONOGRAPH · KDC-MN-275

Enclomiphene

May 9, 2026 Kodiac biolabs Research Revised May 30, 2026 3 min read

Our opinion on this compound

72/100

The clean isomer of clomiphene that took 15 years to almost get approved and still hasnt

Enclomiphene is the compound that should have been straightforward and turned out to be a regulatory saga instead. As the trans-(E)-isomer of clomiphene without the slow-clearing zuclomiphene that drives most of clomiphene's adverse effects, enclomiphene is essentially a cleaner version of the racemic parent compound. Repros Therapeutics took it into multiple phase 3 trials for secondary hypogonadism in men, with the rationale that pure enclomiphene should drive endogenous testosterone production without the visual side effects, mood effects, and residual estrogenic activity that long-term clomiphene exposure produces.

The mechanism is the same SERM hypothalamic feedback story. Antagonism at hypothalamic ER-alpha increases GnRH pulsatility, which drives LH and FSH, which drives endogenous testosterone production. The phase 3 trials (TCC2-101 and TCC2-102 in particular) showed that enclomiphene reproducibly raised testosterone into the normal range in men with secondary hypogonadism while preserving sperm count and luteinizing hormone, which is the differentiated value proposition versus exogenous testosterone therapy.

What we like is the clean isomer pharmacology. Without zuclomiphene the half-life is measured in days, not weeks, so the steady-state behavior is predictable and discontinuation produces relatively rapid clearance. The trial data on testosterone elevation and spermatogenesis preservation is genuinely useful and replicates across studies.

What we dont like is the regulatory history. The FDA issued a complete response letter in 2015 raising concerns about the statistical methodology of the secondary endpoints and clinical-meaningfulness questions, and Repros effectively shelved the program. The compound is FDA approved as Androxal in some descriptions but as of our information that hasnt actually happened formally; the approval status has been stuck for nearly a decade. Brad Anawalt and others have continued some academic work on it.

For research use the compound is genuinely useful as a tool for studying the male HPG axis without the confounds of exogenous testosterone or the slow-clearing zuclomiphene problem of clomiphene. The pharmacokinetics are clean enough to design dose-response studies meaningfully.

Sourcing is moderate. The pure enclomiphene citrate isnt as widely available as clomiphene, and verification of isomeric purity is essential because contamination with zuclomiphene defeats the entire point of choosing this compound over the racemic parent.

Slept-on relative to the underlying pharmacology. Real compound, real evidence, just stuck in regulatory limbo.

Evidence: 75
Mechanism: 85
Reliability: 78
Safety: 75
Sourcing: 65
Value: 70
Signal: 65
Staying power: 60

Plain-language summary Intrigue 62 / 100

Enclomiphene is the pure antagonist isomer of clomiphene, isolated and developed by Repros Therapeutics (as Androxal) for male hypogonadism. By stripping out the estrogenic zuclomiphene component, it offers the testosterone-raising effect of clomiphene without the lingering hot-flash and mood side effects that bother some men on the racemic mixture. Phase 3 trials showed it raised testosterone in obese hypogonadal men while preserving sperm production, a key advantage over standard testosterone replacement. The FDA declined approval in 2016, citing trial design issues, and Repros went bankrupt. It remains popular in men's-health clinics for fertility-preserving testosterone boosting and as post-cycle therapy. Not stocked by Kodiac. This monograph is provided for research and educational reference.

Intrigue 0–100 blends mechanism novelty, evidence strength, and translational potential. Kodiac editorial, not peer-reviewed.

Selective estrogen receptor antagonist ((E)-isomer of clomiphene)

The (E)-isomer of clomiphene; a pure ER antagonist without the estrogenic zuclomiphene component, investigated for male hypogonadism.

Abstract

Enclomiphene ((E)-2-[4-(2-chloro-1,2-diphenylvinyl)phenoxy]-N,N-diethylethanamine; CAS 7599-79-3; molecular formula C26H28ClNO; molecular weight 405.96) is the (E)-isomer of clomiphene, a pure ER antagonist developed by Repros Therapeutics for male hypogonadism with the trade name Androxal. The compound antagonizes hypothalamic ER, releasing negative feedback on GnRH; consequent FSH and LH elevation drives endogenous testosterone production by Leydig cells. Distinct from exogenous testosterone replacement, enclomiphene preserves spermatogenesis and testicular volume because the elevated FSH supports continued Sertoli cell function. Phase 3 trials in obese men with secondary hypogonadism demonstrated efficacy in restoring eugonadal testosterone and improving spermatogenic parameters; the FDA declined approval (twice, 2015 and 2016) citing CMC and clinical pharmacology concerns rather than efficacy. The compound has been licensed and is in development at Cosette Pharmaceuticals. Plasma half-life is approximately 30 hours, much shorter than the 30-day zuclomiphene half-life. Used as the canonical pure SERM antagonist for male hypogonadism research and as PCT.

Mechanism of action

Pure ER antagonist ((E)-isomer of clomiphene); hypothalamic ER blockade increases FSH/LH and consequent endogenous testosterone with preserved spermatogenesis.

Reported research dose ranges

Trial doses 12.5 to 25 mg in the published literature; off-label PCT 12.5 to 25 mg. Rodent studies 1 to 10 mg/kg.

References

Wiehle RD, et al. Enclomiphene citrate stimulates testosterone production while preventing oligospermia. Fertil Steril 2014.
Kaminetsky J, et al. Oral enclomiphene citrate stimulates the endogenous production of testosterone and sperm counts in men with low testosterone. J Sex Med 2013.
Wiehle RD, et al. Pharmacology of enclomiphene citrate in male hypogonadism. Endocr Rev 2014.

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KDC-MN-275

The full reference document is provided strictly for research use only. It reports research dose ranges from the published literature, not instructions for use in humans or animals.

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Enclomiphene

Abstract

Mechanism of action

Reported research dose ranges

References

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Abstract

Mechanism of action

Reported research dose ranges

References

Read the full monograph

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