Enclomiphene Citrate for Secondary Hypogonadism: Evidence, Risks, and Trade-offs

What enclomiphene does

Enclomiphene is an oral selective estrogen receptor modulator (SERM). It blocks estrogen receptors in the pituitary, where estrogen normally restrains the pituitary-testis axis, so the pituitary releases more LH and FSH; those signals tell the testes to produce more testosterone and to keep producing sperm [4]. It is aimed at secondary (hypogonadotropic) hypogonadism, where the testes are healthy but under-stimulated, and it would not be expected to work in primary hypogonadism, where the testes themselves are failing [4]. Oral doses peak about 2 to 3 hours after a dose, with a half-life of about 10 hours [4].

Diagnosis comes first. Both major guidelines require symptoms plus repeated low morning testosterone measurements before treatment is considered, and LH and FSH are then used to work out the cause [8][9].

What the phase 3 trials found

The main evidence is the sponsor's phase 3 program, whose results are posted on ClinicalTrials.gov; no peer-reviewed journal paper was found for them. ZA-301 randomized 151 overweight men aged 18 to 60 with acquired hypogonadotropic hypogonadism (morning testosterone under 300 ng/dL) and normal sperm concentration to enclomiphene 12.5 mg, 25 mg or placebo for 12 weeks. Pooled across the two active doses, 78.8% of men (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, against a pre-set success bar of a lower confidence limit of at least 67%; FDA did not require a placebo comparison for this endpoint [1]. ZA-302 used the same design in 181 men (112 on 12.5 mg, 22 on 25 mg, 47 on placebo), and 81.3% (95% CI 73.9 to 87.0, n=134) reached the normal range [2].

Two further phase 3 studies, ZA-304 and ZA-305, compared enclomiphene with AndroGel 1.62% in overweight men aged 18 to 60 over 16 weeks. Total testosterone rose in every treatment group; LH and FSH rose with enclomiphene and fell with the gel; sperm concentration stayed in the normal range on enclomiphene while there was a marked reduction in spermatogenesis on the gel. The published abstract gives no numerical results [3].

Earlier studies were smaller. The phase 2 dose-finding study enrolled 48 men and compared 6.25, 12.5 and 25 mg daily with AndroGel for 6 weeks; testosterone and LH rose with enclomiphene [6]. A randomized phase 2 trial found enclomiphene raised morning testosterone, estradiol and LH to levels similar to 1% testosterone gel, raised FSH and LH, and preserved sperm counts [10]. An open-label study of 12 men previously on topical testosterone reported total testosterone of 545 (gel) and 525 (enclomiphene) at 6 months, with the abstract giving the unit as pg/dL, sperm counts rising in all 7 men on enclomiphene at 3 months, and no man on gel above 20 million/mL at 3 months [11].

A 2025 meta-analysis of randomized trials of SERMs (clomiphene and enclomiphene pooled) in men with functional hypogonadism found total testosterone a mean 273.76 ng/dL higher than placebo (95% CI 191.87 to 355.66), with high heterogeneity (I2 89%), and no significant difference against testosterone gel [12].

The missing piece: symptoms

The phase 3 program measured hormones and semen, not whether men felt better. When FDA set out its expectations for trials in secondary hypogonadism in 2018, it said it is unclear whether raising testosterone in this population produces clinical benefit, that trials should show meaningful improvement in at least one symptom or sign, and that changes in semen parameters alone are not enough to establish efficacy [4]. EMA's refusal of EnCyzix made the same point: the studies showed higher testosterone but did not examine whether symptoms such as bone strength, weight gain, impotence or libido improved [5].

Why regulators said no

Repros Therapeutics filed a new drug application for enclomiphene (Androxal) for secondary hypogonadism in fertile men. In 2015 Repros announced a complete response letter which, as FDA summarizes it, said the design of the phase 3 studies was not adequate to demonstrate clinical benefit and raised concerns about study entry criteria, titration and bioanalytical method validation. No approval has followed [4]. FDA's advisory-committee materials state plainly that no FDA-approved drugs contain enclomiphene as an active ingredient [4].

In Europe, the CHMP adopted a negative opinion on 25 January 2018 recommending refusal of a marketing authorisation for EnCyzix (enclomifene), applied for by Renable Pharma Limited, for hypogonadotropic hypogonadism in overweight men with a BMI of at least 25. The committee's reasons were that the studies showed higher testosterone but did not look at whether symptoms improved, and that there is a risk of venous thromboembolism. The assessment rested on 4 main studies in 588 patients [5].

A 2026 British Society of Sexual Medicine position statement notes that enclomiphene is not approved by FDA or EMA, that its manufacturer discontinued development in 2021, and advises use only by experienced clinicians in specialist or research settings because long-term efficacy and safety data are lacking [13].

How it is supplied

No FDA-approved enclomiphene product exists. Enclomiphene has no USP monograph and is not on FDA's final list of bulk substances that can be used in compounding; 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. That is an enforcement-discretion policy, not an approval and not a finding that the product is safe or effective [7]. At the 8 June 2022 meeting of FDA's Pharmacy Compounding Advisory Committee, FDA proposed that enclomiphene citrate not be added to the allowed list; the committee voted 4 yes, 8 no, 0 abstain, with members who voted no citing a lack of clinical efficacy evidence [14]. Enclomiphene is not on FDA's list of bulk substances that raise significant safety risks, and compounded enclomiphene products have not been reviewed by FDA for safety, effectiveness or quality [15].

HealthRX.com offers compounded enclomiphene by prescription.

What it does to sperm

The 2026 BSSM statement calls enclomiphene promising for men with secondary hypogonadism who want to preserve fertility, while noting that the evidence comes from small short-term studies and does not support routine use outside specialist settings [13]. In ZA-304 and ZA-305, sperm concentration stayed in the normal range on enclomiphene while spermatogenesis fell markedly on testosterone gel [3], and the phase 2 trials reported the same pattern [10][11].

Preserved on average is not preserved in everyone. 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% [1][2].

Testosterone replacement, by contrast, suppresses sperm production: the Endocrine Society guideline recommends against starting testosterone in men who are planning fertility in the near term [8], and the AUA guideline includes statements for men interested in preserving fertility [9].

Risks and side effects

In the phase 3 and EMA data the most frequent side effects were headache, hot flushes, nausea and muscle spasm, and the reasons men stopped treatment included blurred vision, muscle spasm, headache and aggression. In the 12-week ZA-302, headache was reported by 7 of 112 men on 12.5 mg versus 1 of 47 on placebo, and nausea by 4 of 112 versus 3 of 47 [2].

The safety concerns FDA listed in 2022, drawn from published trials, adverse event reports and EMA's review, were cardiac and thromboembolic events (including pulmonary embolism and deep vein thrombosis in a safety study), raised estradiol, raised PSA, raised hematocrit, and the absence of long-term safety data. EMA noted a slightly higher rate of cardiac and thromboembolic events than with testosterone, and cataracts seen in nonclinical studies (not conclusively linked in people) led the committee to ask for ocular monitoring [4].

The following label warnings are for clomiphene, the mixture, and have not been established for enclomiphene alone. The clomiphene label says blurring and other visual symptoms such as spots or flashes may occur, are usually reversible, but that cases of prolonged visual disturbance have been reported, some after treatment stopped, and that the disturbances may be irreversible, especially with higher dose or longer therapy. It calls for a complete ophthalmological evaluation promptly for any visual symptoms [16]. The same label lists contraindications for clomiphene: liver disease, uncontrolled thyroid or adrenal dysfunction, an organic intracranial lesion such as a pituitary tumour, and pregnancy [16].

Athletes should note that WADA's 2026 Prohibited List names clomifene under S4.2 anti-estrogenic substances and describes that class as including, but not limited to, named substances. Enclomiphene is an isomer of clomifene and should be treated as prohibited, with the athlete's anti-doping organisation the place to confirm [17].

Enclomiphene versus testosterone replacement

Testosterone products are FDA-approved for men who lack testosterone or have low levels together with an associated medical condition, such as testicular failure or a hypothalamus or pituitary problem, and they come as gels, patches, a buccal system and injections [18]. Enclomiphene has no approved label, no standard dose and no long-term safety record [4].

In the head-to-head phase 3 studies, LH and FSH rose with enclomiphene and fell with testosterone gel, and sperm concentration was better preserved on enclomiphene [3]. The 2025 meta-analysis found no significant difference in total testosterone between SERMs and testosterone gel [12]. These studies do not show symptom benefit for enclomiphene, and they do not settle which treatment is preferable for a man without a fertility goal. The clot and cardiac questions raised by regulators remain open [4][5].

Enclomiphene versus clomiphene

Clomiphene citrate is a mixture of two geometric isomers, enclomiphene (trans) and zuclomiphene (cis); per FDA, the USP monograph gives the enclomiphene content of clomiphene as 50 to 70 percent. They are related but not the same drug [4]. Zuclomiphene is the more estrogenic of the two, enclomiphene the more anti-estrogenic, pro-gonadotropic isomer [13]. The clomiphene label notes that zuclomiphene has a longer half-life than enclomiphene and that detectable zuclomiphene persisted for longer than a month in single-dose studies [16]. In 15 men on long-term clomiphene 25 mg daily, median serum enclomiphene was 2.2 ng/mL and zuclomiphene 44.0 ng/mL, a ratio of about 20 to 1 [19].

A 2024 retrospective review of 66 men at one academic center who took clomiphene and later enclomiphene found a median testosterone rise of 166 ng/dL with enclomiphene versus 98 ng/dL with clomiphene (P=0.20), an estradiol change of -5.92 versus +17.50 pg/mL (P=0.001), and fewer side effects on enclomiphene (odds ratio 0.18, 95% CI 0.07 to 0.44). It was not randomized [20].

Clomiphene is FDA-approved only for ovulatory dysfunction in women who want to become pregnant. Its label has no male indication and states that there are no adequate or well-controlled studies demonstrating effectiveness in male infertility, and that testicular tumours and gynecomastia have been reported in men using clomiphene, with cause and effect not known. Use of clomiphene in men with low testosterone is off-label [16].

Dose in the trials

No FDA-approved dose exists [4]. The phase 2 dose-finding trial studied 6.25, 12.5 and 25 mg once daily for 6 weeks [6]. The phase 3 protocols used 12.5 mg once daily, increasing to 25 mg at week 6 if morning testosterone remained below 300 ng/dL [1].