Enclomiphene Citrate Off-Label Uses: Evidence Levels, Mechanisms, and Clinical Applications

What is enclomiphene and how does it work?

Enclomiphene is an oral selective estrogen receptor modulator. It blocks estrogen receptors in the pituitary, where estrogen normally restrains the pituitary-testis axis, so the pituitary releases more LH and FSH. LH drives testosterone production in the testes and FSH supports sperm production [1]. That fits secondary (hypogonadotropic) hypogonadism, where the testes are healthy but under-stimulated. It would not be expected to work in primary hypogonadism, where the testes themselves have failed [1].

After an oral dose, enclomiphene peaks in the blood at 2 to 3 hours, has a half-life of about 10 hours, is metabolised mainly to 4-hydroxy enclomiphene and is excreted mainly in faeces [1].

Enclomiphene is not simply purified clomiphene. Clomiphene citrate is a mixture of two isomers, enclomiphene (trans) and zuclomiphene (cis), and FDA notes that the USP monograph gives enclomiphene content of clomiphene as 50 to 70 percent [1]. Zuclomiphene is the more estrogenic of the two [3], and the Clomid label states that detectable zuclomiphene persisted for longer than a month in single-dose studies [10]. Enclomiphene and clomiphene are related drugs, not the same drug [1].

Is secondary hypogonadism the most studied use?

Secondary hypogonadism means testosterone is low because the pituitary is not signalling the testes strongly enough, not because the testes have failed. The evidence includes three published phase 2 trials [5][11][12], two published phase 3 comparisons against testosterone gel [4], and two phase 3 trials whose results are posted on ClinicalTrials.gov only [6][7].

ZA-301 (NCT01532414) randomised 151 overweight men aged 18 to 60 with morning testosterone below 300 ng/dL and normal sperm concentration to enclomiphene 12.5 mg, 25 mg or placebo for 12 weeks. Pooled across doses, 78.8% (95% CI 70.3 to 85.3, n=113) reached an average 24-hour testosterone in the normal range of 300 to 1040 ng/dL. The pre-set success bar was a lower confidence limit of at least 67%, and FDA did not require a placebo comparison for that endpoint [6].

ZA-302 (NCT01739595) used the same design in 181 men: 81.3% (95% CI 73.9 to 87.0, n=134) reached the normal range [7].

ZA-304 and ZA-305 (BJU Int 2016) compared two enclomiphene doses with AndroGel 1.62% over 16 weeks in overweight men with morning testosterone of 300 ng/dL or lower. Total testosterone rose in every treatment group; LH and FSH rose on enclomiphene and fell on the gel; sperm concentration stayed in the normal range on enclomiphene while spermatogenesis fell markedly on the gel [4].

The earlier phase 2 programme fits the same picture. A 48-man dose-finding study found testosterone and LH rose with 6.25, 12.5 and 25 mg daily over 6 weeks [5]. A comparison with 1% testosterone gel found enclomiphene raised morning testosterone, estradiol and LH to levels similar to the gel, raised FSH and LH, and preserved sperm counts [11]. A 12-man study found sperm counts rose in 7 of 7 men on enclomiphene at 3 months, while the gel did not raise counts above 20 million/mL in any of 5 men at 3 months [12].

A 2025 meta-analysis of randomised trials of clomiphene and enclomiphene together in men with functional hypogonadism found total testosterone 273.76 ng/dL higher than placebo (95% CI 191.87 to 355.66) with high heterogeneity (I2 89%), and LH and FSH higher than placebo. There was no significant difference in testosterone versus testosterone gel [13].

Clinical studies have not established improvement in symptoms or quality of life. FDA's 2018 guidance on secondary hypogonadism says it is unclear whether raising testosterone in this group produces clinical benefit, that trials should show meaningful improvement in at least one symptom or sign, and that semen-parameter changes alone are not enough [1]. EMA's refusal of EnCyzix turned on the same point: the studies showed higher testosterone but did not examine whether symptoms such as bone strength, weight gain, impotence or libido improved [2]. FDA's 2015 complete response letter also said the phase 3 design was not adequate to demonstrate clinical benefit and raised concerns about entry criteria, titration and bioanalytical method validation [1].

Does enclomiphene preserve sperm production?

Partly. In ZA-301, sperm concentration fell by 50% or more in 14.2% of men on enclomiphene versus 2.6% on placebo; in ZA-302 the figures were 14.2% versus 4.3% [6][7]. That is a minority of users, not none.

Against testosterone the contrast is sharper. Sperm concentration stayed within the normal range on enclomiphene while spermatogenesis fell markedly on AndroGel 1.62% [4], and the phase 2 comparison with 1% gel found sperm counts preserved [11]. In the 12-man study counts rose in all 7 men on enclomiphene at 3 months, and testosterone returned to pre-treatment levels one month after stopping [12]. A 2026 British Society of Sexual Medicine position statement calls enclomiphene promising for men with secondary hypogonadism who want to preserve fertility, while noting the evidence comes from small, short-term studies and not recommending routine use outside specialist settings [3].

How does enclomiphene compare with clomiphene?

One retrospective study at a single academic centre followed 66 men who took clomiphene and later enclomiphene. Median testosterone rose 166 ng/dL on enclomiphene versus 98 ng/dL on clomiphene (P=0.20), estradiol fell 5.92 pg/mL on enclomiphene versus rising 17.50 pg/mL on clomiphene (P=0.001), and adverse effects were less frequent with enclomiphene (odds ratio 0.18, 95% CI 0.07 to 0.44). The study was not randomised, so the comparison is suggestive rather than definitive [14].

For context on the older drug: clomiphene citrate is FDA-approved only for ovulatory dysfunction in women who want to become pregnant. Its label states there are no adequate or well-controlled studies demonstrating effectiveness in male infertility, and that testicular tumours and gynaecomastia have been reported in men taking it, with cause and effect not established [10].

What about the other uses people ask about?

Overweight and obesity. The phase 3 trials enrolled overweight men [6][4], and EMA's application was specifically for hypogonadotropic hypogonadism in overweight men with a BMI of at least 25, assessed on four main studies in 588 patients [2]. That population is where the data sit.

Athletes. WADA's 2026 Prohibited List names clomifene in class S4 (hormone and metabolic modulators, prohibited at all times) as an anti-estrogenic substance and SERM. Enclomiphene is not named separately, but the list is written as including, but not limited to, and enclomiphene is an isomer of clomifene, so athletes should treat it as prohibited and check with their anti-doping organisation [9].

What safety issues did regulators flag?

FDA's 2022 review, drawing on published trials, adverse event reports and EMA's assessment, listed cardiac and thromboembolic events (including pulmonary embolism and deep vein thrombosis in a safety study), raised estradiol, raised PSA, raised haematocrit and the absence of long-term safety data. EMA noted a slightly higher rate of cardiac and thromboembolic events than with testosterone; cataracts appeared in animal studies without a confirmed link in people, and EMA wanted ocular monitoring [1].

In the phase 3 and EMA data the most frequent side effects were headache, hot flushes, nausea and muscle spasm, and reasons for stopping included blurred vision, muscle spasm, headache and aggression. In ZA-302, headache occurred in 7 of 112 men on 12.5 mg versus 1 of 47 on placebo, and nausea in 4 of 112 versus 3 of 47 [7].

The Clomid label's warnings describe the mixture, not enclomiphene alone: visual symptoms such as blurring, scotomata and flashes are usually reversible but may rarely persist, and the drug is contraindicated in liver disease, uncontrolled thyroid or adrenal dysfunction, pituitary tumour and pregnancy [10]. The label's clinical trial table lists visual symptoms in 1.5% of patients [10].

Is enclomiphene approved, and what is its regulatory status?

FDA's advisory committee presentation of 8 June 2022 states that no FDA-approved drugs contain enclomiphene as an active ingredient, and it is not approved in the EU either [1][2]. The sponsor, Repros Therapeutics, filed a new drug application for Androxal for secondary hypogonadism in fertile men; FDA issued a complete response letter in 2015 and no approval has followed [1]. EMA's CHMP adopted a negative opinion on 25 January 2018 recommending refusal of EnCyzix (Renable Pharma Limited) for hypogonadotropic hypogonadism in overweight men [2]. The British Society of Sexual Medicine notes that the manufacturer discontinued development in 2021 [3].

Because there is no approved product, no USP monograph for enclomiphene, and no place on FDA's final list of bulk substances that can be used in compounding, pharmacies cannot simply compound it as a routine matter. FDA's list (updated 14 May 2026) places enclomiphene citrate in Category 1, 'Bulk Drug Substances Under Evaluation'. FDA says it does not intend to take action against a compounder using a Category 1 substance if the conditions in its guidance are met, which is enforcement discretion rather than approval or a finding of safety or effectiveness [8]. At the June 2022 Pharmacy Compounding Advisory Committee meeting FDA proposed not adding it, and the committee voted 4 yes, 8 no, 0 abstentions [15]. Enclomiphene is not on FDA's Category 2 list of bulk substances that may present significant safety risks, and compounded enclomiphene has not been reviewed by FDA for safety, effectiveness or quality [16].