Enclomiphene Citrate Monitoring for Young Adults (Ages 18 to 29)

What regulators and medical societies say

Enclomiphene is not FDA-approved, and FDA's advisory-committee material from June 2022 states that no FDA-approved drugs contain enclomiphene as the active ingredient [1]. EMA's committee recommended refusing marketing authorisation for EnCyzix (enclomifene) in January 2018 [5].

The nearest thing to guidance is a 2026 British Society of Sexual Medicine position statement. It says enclomiphene is not approved by FDA or EMA, that its manufacturer discontinued development in 2021, and that it should be used only by experienced clinicians in specialist or research settings because long-term efficacy and safety data are lacking [8].

What the two 12-week trials actually checked

ZA-301 (NCT01532414) randomised 151 overweight men aged 18 to 60 with secondary hypogonadism to enclomiphene 12.5 mg, 25 mg or placebo for 12 weeks [2]. ZA-301 measured whether average 24-hour testosterone reached the normal range of 300 to 1,040 ng/dL, with a pre-set success bar that the lower confidence limit had to reach at least 67% [2]. Pooled enclomiphene: 78.8% (95% CI 70.3 to 85.3, n=113) [2]. ZA-302 used the same design in 181 men and reported 81.3% (95% CI 73.9 to 87.0, n=134) [9]. Both results are ClinicalTrials.gov postings.

Neither trial established that enclomiphene improves symptoms. EMA's refusal noted the studies showed higher testosterone with enclomiphene but did not look at whether symptoms such as bone strength, weight gain, impotence or libido improved [5], and FDA's 2018 guidance on secondary hypogonadism says it is unclear whether raising testosterone in this population gives clinical benefit [1].

Baseline tests the guidelines describe

The diagnostic standard comes from guidelines, not from enclomiphene research. The Endocrine Society's 2018 guideline says to diagnose hypogonadism only in men with symptoms and signs plus unequivocally and consistently low testosterone, to start with a fasting morning total testosterone on an accurate assay, and to repeat it to confirm; free testosterone is recommended when the total is near the lower limit of normal or SHBG is altered [10]. The 2018 AUA guideline describes the same core approach of assessing total testosterone together with symptoms and signs before treatment and monitoring on treatment [11].

Sperm testing at the start is what the enclomiphene trials themselves did. In the two phase 3 studies against testosterone gel, men provided semen samples twice to enrol and twice at the end of the study [3].

The label closest to this space is the clomiphene citrate label, and clomiphene is a mixture of enclomiphene and zuclomiphene, not the same drug [1]. That label covers ovulation induction in women and has no male indication; it states that there are no adequate or well-controlled studies demonstrating effectiveness in male infertility, and that testicular tumors and gynecomastia have been reported in men using clomiphene, with cause and effect not known [12]. Its contraindications include liver disease, uncontrolled thyroid or adrenal dysfunction, pituitary tumor and pregnancy [12]. Those are clomiphene's contraindications and have not been established for enclomiphene alone.

Week 6 and the checks after it

The timed checkpoint in the phase 3 protocols is a trial rule. The phase 3 protocols started at 12.5 mg once daily and up-titrated to 25 mg daily at week 6 if morning testosterone stayed below 300 ng/dL [2]. That is how the studies were run, not a clinical standard that anyone has approved.

The trials drew early-morning serum testosterone [3]. For context on timing, oral enclomiphene is absorbed quickly, peaking 2 to 3 hours after a dose, with a half-life of about 10 hours and excretion mainly in faeces [1]. Outcomes in the phase 3 studies were read at 12 weeks [2][9] and at 16 weeks in the comparison against testosterone gel [3].

Estradiol, hematocrit and PSA

FDA's 2022 review listed raised estradiol, raised PSA, raised hematocrit, cardiac and thromboembolic events including pulmonary embolism and deep vein thrombosis in a safety study, and the absence of long-term safety data [1]. EMA noted a slightly higher rate of cardiac and thromboembolic events than with testosterone, and cataracts in nonclinical studies that were not conclusively linked in people; EMA wanted ocular monitoring [1].

A retrospective study of 66 men who took clomiphene and later enclomiphene found estradiol changed by -5.92 pg/mL on enclomiphene versus +17.50 pg/mL on clomiphene (P=0.001), with a median testosterone rise of 166 versus 98 ng/dL (P=0.20) and fewer side effects on enclomiphene (odds ratio 0.18, 95% CI 0.07 to 0.44) [13]. It was a single-centre review, not a randomised trial.

Sperm counts and fertility

In the two phase 3 studies against AndroGel 1.62%, total testosterone rose in all treatment groups, LH and FSH rose with enclomiphene and fell with the gel, and sperm concentration stayed in the normal range on enclomiphene while there was a marked reduction in spermatogenesis on the gel over 16 weeks [3]. A phase 2 trial found enclomiphene raised morning testosterone, estradiol and LH to levels similar to 1% testosterone gel while FSH and LH rose and sperm counts were conserved [4]. In a 12-man study, sperm counts rose in 7 of 7 men on enclomiphene at 3 months, the gel did not raise counts above 20 million/mL in any of 5 men at 3 months, and testosterone fell back to pre-treatment values one month after stopping [14].

Sperm concentration still fell by 50% or more in some men on enclomiphene: 14.2% versus 2.6% on placebo in ZA-301 [2] and 14.2% versus 4.3% in ZA-302 [9]. Separately, the Endocrine Society guideline recommends against starting testosterone therapy in men planning fertility in the near term [10].

Side effects reported in the trials

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 [9]. In 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 [9].

The clomiphene label warns that blurring, spots or flashes may occur, that these are usually reversible, and that prolonged and possibly irreversible visual disturbance has been reported [12]. That warning belongs to the clomiphene label, which covers the mixture rather than enclomiphene alone.

Doses used in the research

There is no approved dose [1]. A phase 2 dose-finding trial tested 6.25, 12.5 and 25 mg once daily for 6 weeks in 48 men [6], and the phase 3 protocols used 12.5 mg daily with up-titration to 25 mg at week 6 if morning testosterone stayed below 300 ng/dL [2].

Regulatory status and what it means day to day

Enclomiphene has no approved product, no USP monograph and is not on FDA's final list of bulk substances for compounding, so it cannot simply be compounded as a routine matter [15]. FDA's list places enclomiphene citrate in Category 1, substances under evaluation, and FDA says it does not intend to act against a compounder meeting its guidance conditions; that is enforcement discretion, not approval [15]. At the June 2022 advisory committee, FDA proposed not adding it to the allowed list and the vote was 4 yes, 8 no [16]. Compounded enclomiphene is not FDA-approved and has not been reviewed by FDA for safety, effectiveness or quality [17].

For athletes, WADA's 2026 Prohibited List puts anti-estrogenic substances and SERMs such as clomifene in class S4, banned at all times, and the list is described as including but not limited to the named drugs; enclomiphene is not named separately, but it is an isomer of clomifene, so athletes should treat it as prohibited and check with their anti-doping organisation [7].