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Enclomiphene Citrate Super-Responder Profile: Who Gets the Best Results?

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At a glance

  • Drug class / oral selective estrogen receptor modulator, the trans-isomer of clomiphene; not FDA-approved [3]
  • Who responds / men with secondary hypogonadism; not expected to work in primary testicular failure [3]
  • Share reaching normal testosterone / 78.8% in ZA-301 and 81.3% in ZA-302, both 12-week phase 3 trials [1][2]
  • Doses studied / phase 3 protocols used 12.5 mg daily, raised to 25 mg at week 6 if morning testosterone stayed under 300 ng/dL [1]
  • Sperm / 50% or greater fall in concentration in 14.2% of men on enclomiphene in both trials [1][2]

Who responds at all

Enclomiphene blocks estrogen receptors in the pituitary, so the pituitary releases more LH and FSH, which stimulates the testes [3]. Both 12-week trials enrolled overweight men aged 18 to 60 with morning testosterone under 300 ng/dL and normal sperm concentration [1][2]; the refused European application covered men with a BMI of at least 25 [4]. Those are entry criteria, not a ranking of who does best.

What the numbers were

In ZA-301, 151 men took 12.5 or 25 mg daily or placebo; pooled across the enclomiphene arms, 78.8% (95% CI 70.3 to 85.3) reached an average 24-hour testosterone of 300 to 1040 ng/dL [1]. ZA-302, same design, 181 men, reached the normal range in 81.3% (95% CI 73.9 to 87.0) [2].

Across randomized trials of clomiphene and enclomiphene together, SERM therapy raised total testosterone by a mean 273.76 ng/dL over placebo (95% CI 191.87 to 355.66), with high heterogeneity (I2 89%) [5]. This pooled average does not show how individual men responded or identify a super-responder profile.

In 66 men who took clomiphene and later enclomiphene at one academic centre, the median testosterone rise was 166 vs 98 ng/dL (P=0.20, not statistically significant), estradiol fell 5.92 pg/mL vs a rise of 17.50 pg/mL (P=0.001), and side effects were less frequent on enclomiphene (odds ratio 0.18, 95% CI 0.07 to 0.44); the study was retrospective [6].

What to watch for

FDA listed estradiol changes among the safety concerns reported with enclomiphene, along with raised PSA, raised hematocrit, cardiac and thromboembolic events including pulmonary embolism and deep vein thrombosis, and the lack of long-term safety data [3]. EMA noted a slightly higher rate of cardiac and thromboembolic events than with testosterone [3].

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 [2]. A fall in sperm concentration of 50% or more occurred in 14.2% of men on enclomiphene versus 2.6% on placebo in ZA-301, and 14.2% versus 4.3% in ZA-302 [1][2].

Enclomiphene has no FDA-approved product; FDA lists enclomiphene citrate as a bulk substance under evaluation for compounding, and compounded enclomiphene has not been reviewed by FDA for safety, effectiveness or quality [7][8].

Frequently asked questions

Do younger or leaner men respond better to enclomiphene?
In 15 men on clomiphene 25 mg daily for at least 6 weeks, age, BMI, duration of therapy and serum testosterone did not predict enclomiphene or zuclomiphene blood levels [9]. That study measured drug concentrations, not the size of the testosterone response.
Does a big testosterone rise mean symptoms improve?
Not established. EMA said the studies showed higher testosterone but did not examine whether symptoms such as bone strength, weight gain, impotence or libido improved [4], and FDA's 2018 guidance says semen changes alone cannot establish efficacy [3].
Is enclomiphene FDA-approved?
No. FDA's 2022 advisory committee materials state that no FDA-approved drug contains enclomiphene [3], and EMA refused marketing authorisation for EnCyzix in 2018 [4]. FDA lists enclomiphene citrate as a bulk substance under evaluation for compounding [7].
How fast does testosterone rise on enclomiphene?
The 12-week phase 3 trials measured average 24-hour testosterone rather than week-by-week peaks [1][2]. In 36 men given clomiphene 25 mg daily, mean testosterone rose from 247.6 to 610.0 ng/dL by the first follow-up at 4 to 6 weeks [10], and that was clomiphene, not enclomiphene.

References

  1. Official web page. Official web page
  2. Official web page. Official web page
  3. U.S. Food and Drug Administration. U.S. Food and Drug Administration
  4. Official web page. Official web page
  5. Hohl A, Chavez MP, Pasqualotto E, Ferreira ROM, Sande-Lee SV, Ronsoni MF. Clomiphene or enclomiphene citrate for the treatment of male hypogonadism: a systematic review and meta-analysis of randomized controlled trials. Arch Endocrinol Metab. 2025;69(5). Clomiphene or enclomiphene citrate for the treatment of male hypogonadism: a systematic review and meta-analysis of randomized controlled trials
  6. Saffati G, Kassab J, Orozco Rendon D, Hinojosa-Gonzalez DE, Kronstedt S, Lipshultz LI, et al. Safety and efficacy of enclomiphene and clomiphene for hypogonadal men. Transl Androl Urol. 2024;13(9):1984-1990. Safety and efficacy of enclomiphene and clomiphene for hypogonadal men
  7. U.S. Food and Drug Administration. U.S. Food and Drug Administration
  8. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks | FDA. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks | FDA
  9. Helo S, Mahon J, Ellen J, Wiehle R, Fontenot G, Hsu K, et al. Serum levels of enclomiphene and zuclomiphene in men with hypogonadism on long-term clomiphene citrate treatment. BJU Int. 2017;119(1):171-176. Serum levels of enclomiphene and zuclomiphene in men with hypogonadism on long-term clomiphene citrate treatment
  10. Shabsigh A, Kang Y, Shabsign R, Gonzalez M, Liberson G, Fisch H, et al. Clomiphene citrate effects on testosterone/estrogen ratio in male hypogonadism. J Sex Med. 2005;2(5):716-21. Clomiphene citrate effects on testosterone/estrogen ratio in male hypogonadism
Evidence overview for Enclomiphene Citrate Super-Responder Profile: Who Gets the Best Results?