Enclomiphene Citrate: What to Expect, Week-by-Week First Month

Is there a week-by-week timeline?

No published trial reports what men experience in week 1, 2 or 3. The trials checked hormones at fixed points instead: after the first dose (day 1) and at 6 weeks in a phase 2 dose-finding study [1], at 12 weeks in two phase 3 trials [2][3], and at 16 weeks in the comparison with testosterone gel [4].

The one week-based checkpoint

The phase 3 protocols started men at 12.5 mg once daily and raised the dose to 25 mg at week 6 if morning testosterone was still below 300 ng/dL [2].

What the trials measured at 12 and 16 weeks

ZA-301 randomised 151 overweight men with morning testosterone under 300 ng/dL to 12.5 mg, 25 mg or placebo for 12 weeks. Among men on enclomiphene, 78.8% (95% CI 70.3 to 85.3, n=113) reached an average 24-hour testosterone of 300 to 1040 ng/dL, and sperm concentration fell by 50% or more in 14.2% versus 2.6% on placebo [2]. ZA-302 repeated the design in 181 men: 81.3% (95% CI 73.9 to 87.0, n=134) reached the same range, and a 50% or greater fall in sperm concentration occurred in 14.2% versus 4.3% on placebo [3]. At 16 weeks against AndroGel 1.62%, total testosterone rose in every treatment group, LH and FSH rose with enclomiphene and fell with the gel, and sperm concentration stayed in the normal range on enclomiphene while spermatogenesis fell markedly on the gel [4].

Symptoms are the gap

The trials measured hormones and sperm, not whether men felt better. FDA's May 2018 guidance on secondary hypogonadism, as described by FDA in 2022, says it is unclear whether raising testosterone in this group produces clinical benefit, and that semen changes alone cannot establish efficacy [5]. EMA's January 2018 refusal of EnCyzix said the studies showed higher testosterone but did not examine whether bone strength, weight gain, impotence or libido improved, and noted a venous thromboembolism risk; the review covered 4 main studies in 588 patients [6].

Side effects recorded during treatment

The most frequent were headache, hot flushes, nausea and muscle spasm; reasons men stopped included blurred vision, muscle spasm, headache and aggression [3]. In ZA-302, headache was reported by 7 of 112 men on 12.5 mg versus 1 of 47 on placebo [3]. Raised estradiol is one of the safety concerns FDA listed in 2022 from published trials, adverse event reports and EMA's review [5].

Whose label applies, and the regulatory position

No FDA-approved drug contains enclomiphene. The Clomid label applies to clomiphene citrate, a mixture of enclomiphene and zuclomiphene, a different drug [5][7]. The clomiphene citrate label reports that visual symptoms can be prolonged or irreversible, more likely with higher doses and longer use; this warning is for clomiphene citrate and has not been established for enclomiphene alone [7].

Enclomiphene is not approved in the US or EU [5][6], and FDA sent the sponsor a complete response letter in 2015 citing inadequate phase 3 design [5]. FDA lists enclomiphene citrate as a bulk substance under evaluation, which is enforcement discretion under conditions, not a finding of safety or effectiveness [8].