Enclomiphene

What enclomiphene is and how it works

Enclomiphene is one half of a substance that most readers arrive here already believing they know. Clomiphene citrate is a mixture of two isomers — zuclomiphene, the cis form, and enclomiphene, the trans form — and it is the mixture that carries an approval. Enclomiphene citrate is the trans-isomer isolated and developed separately as a distinct product under the name Androxal, and it did not reach approval.^[10][4] Everything on this page that describes an effect names which of those two things was actually administered, because they are not the same exposure and the published evidence for them is not the same evidence.

Mechanically, enclomiphene is a selective estrogen receptor modulator. Estrogen normally provides negative feedback to the hypothalamus and pituitary; blocking that feedback allows luteinising hormone and follicle stimulating hormone to rise, and the testis responds by producing more testosterone of its own. That is the difference the trials were built to demonstrate: in the phase III programme, gonadotropins rose in the enclomiphene groups and fell in the testosterone gel group, because exogenous testosterone suppresses the same axis that enclomiphene releases.^[1][2]

The isomer distinction is not chemical trivia, and the evidence against reading one across to the other is published. In 15 men who had been taking clomiphene citrate daily for secondary hypogonadism for at least six weeks, median serum concentrations were 44.0 ng/mL of zuclomiphene against 2.2 ng/mL of enclomiphene, a median ratio of 20 to 1. The authors concluded that the two isomers have distinct biochemical and toxicological properties and that the finding supports developing a pure agent rather than relying on the mixture.^[5] Whatever the approved mixture does in a person, it does mostly while the other isomer predominates in serum.

Three further boundaries matter because all four substances appear in the same online conversations. Human chorionic gonadotropin acts a tier lower, directly at the luteinising hormone receptor. Gonadorelin acts a tier higher, at the pituitary. Aromatase inhibitors block the conversion of androgens to estrogens rather than blocking the receptor. Each is a separate molecule with a separate literature, and none of them is enclomiphene.^[10]

What the research actually shows

The scale of the literature is the first fact worth having. A PubMed search for enclomiphene on 1 September 2026 returned 97 records, of which enclomiphene AND randomized controlled trial[pt] returned 3 and enclomiphene AND clinical trial[pt] returned 7. A search for clomiphene AND hypogonadism AND male on the same database on the same day returned 296. This page is written from the 97, and specifically from the three randomized trials within them; the 296 belong to a different substance. Sources here were selected by taking, for each claim area, the registered randomized trials of enclomiphene itself, plus the independent pooled analyses, plus the strongest published counterweight to each — and by admitting retrospective work only for the comparative tolerability claim.

The randomized core is three trials, and all three are sponsor-run. The largest is a pair of parallel randomized, double-blind, double-dummy, placebo-controlled multicentre phase III studies in overweight men aged 18 to 60 with secondary hypogonadism, run over 16 weeks against testosterone gel. Total testosterone rose in every treatment group including the gel comparator; gonadotropins rose on enclomiphene and fell on gel; and sperm concentration was maintained in the normal range on enclomiphene while spermatogenesis was markedly reduced on gel.^[1] A randomized multicentre phase II trial reported the same directional result.^[2] The third is a proof-of-principle study, and its own methods section describes it as open-label with 12 participants in total: at six months, total testosterone was 545 ± 268 on gel and 525 ± 256 in the enclomiphene group as the paper reports them, only the enclomiphene group showed increased gonadotropins, and sperm counts rose in seven of seven men at three months.^[3] A separate randomized, single-blind two-centre study compared three daily amounts against transdermal testosterone in 48 enrolled and 44 per-protocol men and found the highest enclomiphene arm and the gel arm not different from each other on trough testosterone at six weeks, p = 0.23.^[4]

Two independent pooled analyses exist and they answer different questions. A 2023 systematic review and meta-analysis of seven studies and 292 men with obesity-related functional androgen deficiency reported an enclomiphene-specific mean testosterone difference of 7.50 nmol/L (95% CI 6.52 to 8.48) with heterogeneity of I² = 4%, alongside a clomiphene estimate of 11.56 nmol/L with I² = 69%; its comparisons are before-and-after rather than against placebo.^[7] A 2025 systematic review and meta-analysis restricted to randomized trials reported a pooled testosterone difference against placebo of 273.76 ng/dL (95% CI 191.87 to 355.66) with I² = 89%, no significant testosterone difference between these agents and testosterone gel, and concluded they should be considered an alternative to gel — but it pools clomiphene and enclomiphene together, so it is a class estimate rather than a molecule one.^[6]

Where the evidence is weak

The randomized programme is concentrated in one sponsor, and this is the central limitation of the page. Reading the author affiliation block printed in each PubMed record, four of the five named authors of the phase II trial carry the affiliation of the developing company and the fifth is at a university; the only affiliation the pharmacodynamic record prints is the company's, for its first author; the proof-of-principle paper carries the company's copyright line; and three of the nine authors of the isomer-ratio study carry the company's affiliation alongside six academic ones.^[2][4][3][5] The phase III paper's own author block prints three academic and clinical affiliations and no company one, and its PubMed record carries no conflict-of-interest statement — but the trials it reports are registered with that company as their lead sponsor, so it is described here as sponsor-funded work rather than as independent.^[1] The two pooled analyses are the genuinely independent contributions, and both of them are syntheses of the same small set of trials rather than new evidence.^[7][6]

Two completed trials were never reported, and one of them is the one a cautious reader would ask for. The two pivotal phase III studies, each enrolling 120 participants, are recorded on ClinicalTrials.gov as completed with no results posted, so the published paper is the only public account of them and there is no registry record to check it against.^[1] Separately, a 12-month single-blind placebo-controlled phase III study of the effects of enclomiphene citrate on bone mineral density in men with secondary hypogonadism, enrolling 300 participants with bone mineral density at 52 weeks as its primary outcome, is recorded as completed in September 2014 with no posted results; a PubMed search for its registry identifier NCT01619683 on 1 September 2026 returned 0 records. The animal work that does separate the isomers on bone points the uncomfortable way: in ovariectomized rats the benefit of the mixture on non-reproductive tissue was conferred by both isomers, and the two together were more beneficial on bone volume and architecture than either alone.^[11]

Every human endpoint in the randomized literature is a surrogate. Serum testosterone is a laboratory value, not energy, libido, mood or function. Sperm concentration is a fertility surrogate, not a conception. No published randomized trial of this substance reports a pregnancy or a live birth, and a PubMed search for enclomiphene AND randomized controlled trial[pt] on 1 September 2026 returned 3 records, none of which carries a validated symptom instrument as a primary endpoint.^[6] The one retrospective series that looked hardest at semen found volume and concentration unchanged on either substance, with only total motile sperm count separating.^[9]

The durations are short and the comparative data are retrospective. The longest randomized exposure on this page is 16 weeks; the pooled obesity analysis covers 1.5 to 4 months.^[1][7] The head-to-head comparison against the parent mixture is a chart review of 66 men in which the testosterone difference was not significant at P=0.20, and the adverse-event difference that was significant came from the same uncontrolled record set.^[8] The compound-level evidence grade on this page is human RCT evidence, and it is earned by the testosterone and sperm-concentration endpoints of those three published randomized trials and by nothing else — not by symptoms, not by long-term safety, not by bone, and not by any approval.

Legal and regulatory status

There is no FDA-approved enclomiphene product in the United States, and the absence was checked from more than one direction. Queried on 1 September 2026, openFDA drug/drugsfda returned no matches for enclomiphene on products.active_ingredients.name, on openfda.generic_name and on openfda.substance_name, each returning HTTP 404 NOT_FOUND; the drug/label endpoint returned no matches on openfda.generic_name or on openfda.substance_name. In the same session on the same database, a products.active_ingredients.name query for TESTOSTERONE returned 88 applications, so the query shape works and a zero is a real zero.

One search on that database makes enclomiphene look approved and it is worth naming. An unfielded full-text search of drug/label for the word enclomiphene on 1 September 2026 returned 29 records. Reading all 29, every one is a clomiphene citrate product label that mentions the isomer inside its own Description, Clinical Pharmacology or Pharmacokinetics text, and not one is an enclomiphene label. An unfielded hit count is not evidence that a product exists.

Where the substance does appear in FDA data is as a raw material. A national drug code directory query for the generic name enclomiphene on 1 September 2026 returned 24 records, all of them registered as bulk ingredient or bulk ingredient for human prescription compounding, and all 24 in powder form. There is no finished dosage form. Enclomiphene Citrate is listed in FDA's 503A bulk drug substance nomination category lists, in the document self-dated Updated May 14, 2026, under Category 1 — Bulk Drug Substances Under Evaluation. Under evaluation is what it says: it is not an approval, not a compounding authorisation and not a finding of safety or efficacy. The substance appears in none of the three categories of the 503B outsourcing facility bulks list self-dated Updated March 21, 2025, and on neither table of FDA's separate page on bulk drug substances that may present significant safety risks, whose content is stamped current as of 22 April 2026. Each of those null results was run alongside in-document positive controls that did return entries.

Clomiphene citrate's approval is a different product's approval, and the number depends on which field you ask. On 1 September 2026, openFDA drug/drugsfda returned 9 applications for products.active_ingredients.name:"CLOMIPHENE CITRATE" and 5 for openfda.generic_name:"clomiphene citrate". The five are a strict subset of the nine, and the four the generic-name query cannot see include both original new drug applications, NDA 016131 and NDA 018361, each of whose product is in discontinued marketing status; the currently marketed products are abbreviated applications. A count of five would have been a false statement about this molecule, so the field is named here alongside the number.

FDA's orphan drug designation database returned "No records found" for enclomiphene and for clomiphene on 1 September 2026, against a same-session product-name search for testosterone that returned 9 designations. That answer was obtained by submitting the database's own search form in a browser: a scripted request to the results endpoint returned the empty form even for the control, and an HTTP behaviour is a fact about a route rather than about a register. A full-text search of FDA's warning-letter index on 1 September 2026 returned no letters naming enclomiphene, against a same-session sildenafil control that returned results, and openFDA drug/enforcement returned no records.

One boundary on all of the above. An application that was submitted and not approved does not appear in Drugs@FDA at all. So "there is no approved enclomiphene product" is verifiable and is stated here; what happened inside any regulatory submission is not, and is not asserted. A 2019 drug profile discusses the difficulties associated with the FDA approval of a new molecular entity in this area, and that is as far as the published record taken here goes.^[10]

Anti-doping. The 2026 World Anti-Doping Code International Standard Prohibited List, in force from 1 January 2026, was retrieved on 1 September 2026 from the WADA-hosted document linked by the United States Anti-Doping Agency's prohibited-list page. Enclomiphene is not named on it. Searching the whole document, "enclomiphene", "zuclomiphene" and "isomer" return nothing anywhere in section S4. What the List does name, under the international spelling "Clomifene", is the parent mixture, in S4.2 ANTI-ESTROGENIC SUBSTANCES [ANTI-ESTROGENS AND SELECTIVE ESTROGEN RECEPTOR MODULATORS (SERMS)], whose entry list is introduced by the words "Including, but not limited to:". Section S4, headed "S4 HORMONE AND METABOLIC MODULATORS", is "PROHIBITED AT ALL TIMES (IN- AND OUT-OF-COMPETITION)" and states that "Prohibited substances in classes S4.1 and S4.2 are Specified Substances." So enclomiphene's position rests on being a selective estrogen receptor modulator caught by an open-ended class definition, and on being a constituent isomer of a named substance — not on being named, and not on an optical-isomer rule, because the phrase "including all optical isomers" appears in sections S3, S5, S6 and S7 of the 2026 List and does not appear in S4. Section S0, non-approved substances, does not reach it, because S0 covers only a substance "which is not addressed by any of the subsequent sections of the List", and S4.2 addresses it. It is not on the 2026 Monitoring Program, retrieved the same day, whose entries are ecdysterone, gonadotrophin-releasing hormone analogues in females under 18, hypoxen, seven stimulants, seven narcotics and markers of two incretin drugs. The List is reissued annually, so anyone in a tested sport reads the year in force at first hand rather than this page, and absence of a name is never a statement that a substance is permitted.

Peptide Health Lab does not sell anything, does not prescribe, and does not tell anyone where to obtain anything. The regulatory picture appears here only because it changes what the evidence above can and cannot support.

Questions to bring to a provider

The useful questions are the ones that separate a laboratory number from a reason to be in the room at all:

• What symptom, function or fertility goal is this meant to change, and what would count as it not working, given that the randomized trials measured serum hormones and sperm concentration rather than symptoms?^[6]
• If fertility is the goal, is a maintained sperm concentration against a comparator that suppresses it the outcome being sought, and what would a fertility assessment add that a sperm count does not?^[1][9]
• How does the absence of any reported bone-density result bear on a plan measured in years rather than weeks, given that the longest randomized exposure published is 16 weeks?^[1]
• Since the substance has no approved product and is prepared through compounding, what does that change about strength, identity and what is being monitored?
• What is the plan for estradiol, given that the one comparative series reported it moving downward on this isomer and upward on the parent mixture?^[8]
• Is there a reason to expect this to behave like clomiphene, given that in men on the mixture the other isomer predominates in serum at a median ratio of 20 to 1?^[5]
• Which of the alternatives on the same axis is actually being compared here, and on whose evidence?^[10]

A clinician who answers "the trials measured a hormone level, not how you feel" is describing the literature accurately.