Enclomiphene

16 weeks

Two randomized phase 3 trials followed selected overweight men for 16 weeks. Both enclomiphene and topical testosterone gel raised testosterone; enclomiphene maintained sperm concentration while gel suppressed it.^1640,1641

Clinical outcomes

EMA reviewed sexual-function questionnaires in a supportive study, body-composition studies and longer safety exposure. Its 2018 decision was a refusal, with insufficient symptom benefit and important safety concerns.¹⁶⁴¹

Newer reports

The 2023 and 2024 clinical comparisons were retrospective. The 2026 sublingual series used a multi-ingredient product in 15 men without a control group. Their findings belong to those designs and formulations.^{1643,1649,1654}

Muscle, strength and weight

Outcome	Posted comparison
Lean mass	Mean gains were 3.14 and 2.40 kg in the two active groups and 1.05 kg with placebo. Analysis groups were 16, 12 and 12; comparison p-values were 0.7103 and 0.4529.1644
Strength	Chest-press and leg-press strength improved across groups, without a significant active-group advantage in the posted comparisons.1644
Weight	Mean loss was 4.36 and 6.15 kg in the active groups and 14.51 kg with placebo. The comparison p-values were 0.0139 and 0.0225.1644

Read the study with its limits

ZA-205 randomized 50 men, and all groups received diet and trainer support. The registry labels all 20 outcomes primary and reports smaller, varying analysis groups. Its posted BMI and glucose units contain errors.¹⁶⁴⁴

Symptoms, candidacy and strength

01 Who was studied in the main trials?

The two 16-week phase 3 trials studied overweight men aged 18 to 60 with low morning testosterone and low or normal LH. Eligibility was confirmed with repeated laboratory tests. This is the main population behind the hormone and sperm findings.^1640,1641

02 Does it reliably improve libido or erections?

A reliable benefit has not been established. Supportive study ZA-003 used sexual-function questionnaires, but EMA reported consistent libido improvement only with testosterone gel and no enclomiphene benefit over placebo on the other reported questionnaires.¹⁶⁴¹

03 Did it build more muscle than placebo?

The 50-person ZA-205 trial measured lean mass at 48 weeks. Mean increases were 3.14 and 2.40 kg in the two enclomiphene groups and 1.05 kg with placebo, with no statistically significant group advantage. All groups received diet and trainer support.¹⁶⁴⁴

04 Why can testosterone rise without feeling better?

The trials measured a clear hormone response, while patient-important symptom benefits remained uncertain. Supportive ZA-003 measured symptoms and did not show an enclomiphene advantage over placebo on the reported questionnaires. The evidence therefore answers the laboratory question more clearly than the symptom question.¹⁶⁴¹

05 Does it improve mood or cognition?

The 2024 chart review recorded mood-change complaints during clomiphene treatment and none during the following enclomiphene phase. Participants switched without a washout, so carry-over could affect the comparison. Controlled mood or cognitive benefit remains unestablished.^1649,1641

06 Did strength improve more than with placebo?

ZA-205 measured chest-press and leg-press strength at 48 weeks. Both tests improved across groups, without a statistically significant enclomiphene advantage in the posted comparisons. All groups had diet and trainer support.¹⁶⁴⁴

07 Was it better for weight loss?

ZA-205 reported greater mean weight loss with placebo at 48 weeks: 14.51 kg versus 4.36 and 6.15 kg in the enclomiphene groups. The study randomized 50 men, and all groups received diet and trainer support.¹⁶⁴⁴

08 How does enclomiphene raise testosterone?

It alters estrogen feedback through the hypothalamus and pituitary. The studied men generally had increases in LH and FSH, with a rise in their own testosterone production. Testosterone gel acted through a different route and reduced those pituitary signals.^1641,1640

Trial outcomes

01 Which laboratory results did researchers follow?

Studies followed testosterone, LH, FSH, estradiol and semen measurements; some also measured blood counts, lipids, PSA and metabolic markers. A supportive study also used symptom questionnaires.^{1642,1640,1641}

02 Do the early hormone changes last?

The clinical program included six-month studies and extensions, with some participants followed for a year. Hormone increases during treatment are documented. Lasting symptom benefit over years remains an open question.^1641,1645

03 How soon did testosterone change?

The six-week ZA-204 study found testosterone increases within two weeks. That is a laboratory timeline from the studied oral product. A dependable timeline for changes in energy, libido or mood has not been established.¹⁶⁴²

04 Did it increase IGF-1 or growth hormone?

Technical problems prevented growth-hormone measurement in ZA-204. Researchers used IGF-1 as a surrogate, and it decreased during treatment. Growth, recovery and longevity benefits remain unestablished.¹⁶⁴²

05 Is it better than clomiphene?

The 2023 retrospective study found no statistically significant between-treatment difference in changes in its measured hormones or semen parameters. A separate 66-person sequential study reported fewer chart-coded side effects on enclomiphene, with unequal treatment durations and no washout. Neither was a randomized head-to-head trial.^1643,1649

06 Why do trial and paper participant counts differ?

Some publications analyze subsets, and extension studies continue earlier participants. The ZA-201 registry contains 17 people, including a separate five-person washout arm; its paper reports the 12-person gel comparison. Other registry and publication count discrepancies remain documented.^{1657,1648,1641}

07 Are results posted for the 499-person safety study?

Yes. NCT01534208 has posted participant-flow, outcome and adverse-event tables for ZA-300. The 26-week open-label study reports different outcome and safety analysis denominators.¹⁶⁴⁵

08 How independent is the evidence?

Repros sponsored the main development program. Later observational papers came from separate clinical groups, with conflicts and study limitations recorded. Repeated publications and extensions from the same program are counted with their cohort links.^{1641,1643,1649}

09 Did the studies establish a blood-sugar benefit?

ZA-205 measured glucose and HbA1c at 48 weeks alongside shared diet and trainer support. It showed no consistent metabolic advantage over placebo. Source-posted unit errors and small analysis groups limit interpretation.¹⁶⁴⁴

The European decision

01 Why did the European application fail?

CHMP accepted the testosterone increase but found the evidence for meaningful symptom benefit insufficient. It also raised safety concerns, including clot events. The assessment includes a dissenting benefit-risk opinion.¹⁶⁴¹

Approval, compounding and sport

01 Is there an FDA-approved enclomiphene medicine?

The October 2, 2026 named FDA approval and label searches found no matching records. FDA also describes the unsuccessful development application in its 2022 assessment.^1650,1647

02 What does FDA Category 1 mean?

FDA's May 14, 2026 document places enclomiphene citrate in Category 1, under evaluation. Its January 2025 guidance describes nonbinding enforcement discretion when all four circumstances are met: a qualifying Category 1 nomination before January 7, 2025, registered original and subsequent manufacturers, a valid certificate of analysis, and compliance with the other section 503A conditions. The category grants no medicine approval.^1651,1652

03 What did the 2022 compounding committee vote?

The advisory committee voted 4 yes, 8 no and 0 abstain on adding enclomiphene citrate to the 503A list. The vote was advisory; the dated FDA category record and guidance describe the later administrative position.^1653,1651

04 What is its status in tested sport?

The 2026 WADA List, effective January 1, 2026, prohibits S4.2 anti-estrogenic substances including SERMs at all times and names clomifene. The 2027 List takes effect January 1, 2027 and retains that treatment. Neither list names enclomiphene separately, so exact-isomer coverage is a class-and-identity inference.^{1662,1663,1641}

Sperm and reproductive outcomes

01 What happened to sperm counts compared with testosterone gel?

In the two 16-week phase 3 trials, enclomiphene maintained sperm concentration while testosterone gel suppressed it. The combined hormone-and-sperm results favored enclomiphene in those study groups. Pregnancy and live-birth outcomes were not supplied by those trials.^1640,1641

02 Does it improve pregnancy or live-birth chances?

The pivotal program focused on sperm concentration. A newer retrospective comparison measured semen changes. Pregnancy and live-birth benefit remains unestablished.^1647,1643

03 Has isolated enclomiphene been studied in women?

A 1989 study examined separate clomiphene isomers in 19 normally cycling women undergoing donor insemination. Enclomiphene affected follicular development, and both isomers affected sperm-cervical-mucus interaction. This small sequential study is separate from the modern male program.¹⁶⁶¹

Side effects, stopping and interactions

01 Can estradiol rise?

Yes. In the 2023 retrospective study, the 18 men with paired estradiol measurements in the enclomiphene group had a median rise from 29.5 to 67 pg/mL. Other studies reported different changes, so the response varied across populations and study designs.^1643,1644

02 What is known about interactions?

The development program studied drug metabolism and a midazolam interaction. CYP2D6 and CYP3A enzymes are involved, and exposure varied in people with impaired metabolism. Evidence for combinations with other hormones, supplements and recreational drugs remains incomplete.¹⁶⁴¹

03 What happens after treatment stops?

In the small ZA-204 study, testosterone and LH effects persisted for at least one week after treatment ended. In the earlier 12-person comparison, testosterone returned toward pretreatment values one month after stopping. Longer symptom and adverse-effect recovery courses were not established.^1642,1648

04 Were vision problems reported?

The EMA assessment discusses blurred vision and cataract findings and asks for further safety evaluation. The frequency and recovery timeline for current compounded products are uncertain in the accessible evidence.¹⁶⁴¹

05 What side effects did the trials record?

The program recorded headaches and other treatment-emergent events, including vision findings and clot events. In the pivotal pooled safety table, at least one event was reported in 116 of 324 enclomiphene recipients, 38 of 85 gel recipients and 61 of 168 placebo recipients. The table includes events regardless of whether the study drug caused them.¹⁶⁴¹

06 Could it cause or worsen sleep apnea?

Whether enclomiphene causes or worsens sleep apnea remains an evidence gap in the cited program.¹⁶⁴¹

07 What does the atrial-flutter case show?

A 2026 case described atrial flutter after an inadvertent dose increase in a man with previous mitral-valve surgery and structural heart changes. The authors rated drug causality as possible. The case adds a safety report, with major competing explanations.¹⁶⁵⁵

08 Which clot events concerned regulators?

EMA describes three venous clot or pulmonary-embolism cases and one fatal ischemic stroke during enclomiphene exposure. The case histories include other risk factors. Individual reports and overlapping exposure pools cannot provide a dependable rate for current products.¹⁶⁴¹

09 Was anyone followed for a year?

EMA reported 1,403 enclomiphene-exposed people across phase 2 and 3 studies. Of these, 482 received daily treatment for more than 6 months and 116 for at least 12 months. The counts include linked trials and extensions.¹⁶⁴¹

10 Are adverse events being reported now?

In FDA data last updated July 30, 2026, the October 2 named-product queries returned 12 unique spontaneous-report IDs. Four listed an enclomiphene product as suspect, including two combination products, and eight listed concomitant use. These reports lack an exposed-population denominator and do not verify product identity or causation.¹⁶⁶⁴

11 Can liver, kidney function or CYP2D6 affect exposure?

Yes. Clinical pharmacology studies found higher and variable exposure in some impaired-metabolism, kidney and liver groups. EMA requested further information because the data in these populations were limited.¹⁶⁴¹

Identity, formulation and exposure

01 Is enclomiphene the same as clomiphene?

Enclomiphene is one geometric isomer. Clomiphene products contain both enclomiphene and zuclomiphene, which have different exposure patterns. Studies of the mixture are appraised separately.^1646,1647

02 What is its half-life?

EMA reports an 8 to 10 hour plasma elimination half-life for the studied oral enclomiphene product. Human concentration-time profiles are available. Hormone changes can outlast the measured drug exposure.^1641,1642

03 What did the 2026 sublingual study add?

An uncontrolled 15-man series reported higher testosterone after 60 days with a multi-ingredient sublingual formulation. It included boron, vitamin C, spermidine and a proprietary delivery system. The separate contributions and longer-term clinical outcomes are unresolved.¹⁶⁵⁴

04 Is there an approved dose?

The dated FDA searches found no matching approved enclomiphene product or label. Studies used specific oral formulations and supervised protocols. Their doses belong in the research record.^1650,1641

05 How do the base and citrate salt differ?

They have different chemical records and molecular weights: 406.0 for the base and 598.1 for the citrate in PubChem. Study documents may express an amount as base or salt. The formulation and unit basis need to match before amounts can be compared.^1646,1656

06 Did Chinese, Russian or Japanese sources add clinical evidence?

The Chinese process patent describes preparation chemistry, and the Japanese conference abstract examines computational binding. The Russian dissertation used mixed-isomer clomiphene in its human treatment arm. No additional isolated-enclomiphene clinical trial was identified in these appraised records.^{1658,1659,1660}

07 Does a matching chemical name prove a product matches the trials?

A chemical identifier establishes which substance a database record describes. The trial formulation, salt, concentration, purity and delivery route require separate evidence. The cited sources do not establish direct testing of a particular product.^1646,1647