Enclomiphene
The trans-isomer of clomiphene, a nonsteroidal selective estrogen receptor modulator studied as an oral therapy for secondary hypogonadism in men; not a peptide, never approved in the US or EU, and compounded in the US only under FDA's interim enforcement policy.
Also referenced as: Enclomiphene citrate, Enclomifene, trans-clomiphene, Androxal, EnCyzix
Also appears in: Performance
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This name primarily lives in the research market and should not be read like an approved pharmaceutical product.
Primary research area: Hormone. Also surfaces under Performance for browsing and discovery.
Where the compound acts, as a browse axis. It is an editorial grouping for discovery, not a claim about labeled indications.
Enclomiphene citrate, Enclomifene, trans-clomiphene, Androxal, EnCyzix
No FDA label signal · 286 trials · 98 PubMed results
Enclomiphene has name-matched human trials with published or reported controlled evidence, but is not FDA-approved. The research is real and ongoing — treat findings as developing rather than settled.
Enclomiphene has 2 name-matched clinical trials (highest phase: Phase 3) and 98 PubMed-indexed publications and is not FDA-approved. Human trials are registered but none have posted results yet.
Re-checked nightly against the registries — tracked since 2026-10-28. No band changes yet.
Grades evidence strength, not efficacy or safety. Research-use context; not medical advice. Graded 2026-11-02 from PubMed, ClinicalTrials.gov, ISRCTN, openFDA, Health Canada, and OpenAlex — computed deterministically and refreshed nightly, with a retraction check. How we grade →
What is Enclomiphene?
Enclomiphene is the trans (E) geometric isomer of clomiphene, a nonsteroidal triphenylethylene selective estrogen receptor modulator (SERM). It is a small molecule, not a peptide; it appears in peptide-adjacent research catalogs and telehealth clinics because it raises endogenous testosterone through the hypothalamic-pituitary axis, which places it next to gonadorelin, hCG and kisspeptin in “testosterone restoration” discussions. Clomiphene citrate, the FDA-approved ovulation-induction drug, is a fixed mixture of enclomiphene and its cis (Z) isomer zuclomiphene, roughly 60:40; enclomiphene was developed as a single-isomer oral product (Androxal, later EnCyzix) for secondary hypogonadism in men, but no regulator has approved it.
How it works
- Estrogen receptor antagonism at the hypothalamus and pituitary removes estradiol negative feedback, increasing gonadotropin output. In a randomized, single-blind Phase II study of 48 men, all three enclomiphene doses (6.25, 12.5 and 25 mg daily) raised total testosterone into the normal range while pushing LH and FSH above it, whereas transdermal testosterone raised testosterone while suppressing LH (Wiehle et al., BJU International, 2013)
- Rising LH and FSH preserve spermatogenesis. In two parallel Phase III studies, enclomiphene maintained sperm concentration in the normal range over 16 weeks while testosterone gel produced a marked reduction (Kim et al., BJU International, 2016)
- The two clomiphene isomers behave differently. Zuclomiphene is more estrogen-agonist-leaning and clears far more slowly: in 15 men on long-term clomiphene 25 mg daily the median zuclomiphene-to-enclomiphene serum ratio was 20:1 (Helo et al., BJU International, 2017), and in a chronic oral-gavage study in male mice zuclomiphene, but not enclomiphene, produced profound effects on Leydig cells, epididymis, seminal vesicles and kidneys (Fontenot et al., BJU International, 2016). Separating out the trans-isomer is the entire rationale for the single-isomer product
- Pharmacokinetics: the only single-dose isomer study in patients (nine infertile women with polycystic ovary syndrome given 50 mg clomiphene) measured an enclomiphene AUC roughly twenty-fold lower than zuclomiphene’s, because enclomiphene is cleared within days while zuclomiphene has a very flat terminal phase and a long residence time (Ghobadi et al., Journal of Clinical Pharmacology, 2009). Men-specific single-isomer pharmacokinetics come from the Repros Phase II work above
Research status
Enclomiphene’s clinical program was run by Repros Therapeutics between 2006 and 2017 and has been dormant since.
- Phase II: Kaminetsky et al., Journal of Sexual Medicine, 2013;10(6):1628–35 (open-label Phase IIb, 12 men previously on testosterone gel; testosterone and sperm counts rose); Wiehle et al., BJU International, 2013;112(8):1188–200 (pharmacodynamics and pharmacokinetics, 48 men); Wiehle et al., Fertility and Sterility, 2014;102(3):720–7 (ZA-203, NCT01270841, 83 men randomized against placebo and testosterone gel; sperm counts conserved)
- Phase III: ZA-300, a six-month open-label escalating-dose safety study (NCT01534208, 499 men); ZA-301 (NCT01532414, 151 men) and ZA-302 (NCT01739595, 181 men), placebo-controlled morning-testosterone normalization studies in overweight men with acquired hypogonadotropic hypogonadism; ZA-304 (NCT01993212) and ZA-305 (NCT01993225) against testosterone gel, published as Kim et al., BJU International, 2016;117(4):677–85; plus a six-month open-label extension (NCT01739582). Every efficacy endpoint was biochemical: morning testosterone, LH, FSH and sperm concentration
- FDA: the NDA was submitted on February 2, 2015 and accepted for review that April. The advisory committee scheduled for November 3, 2015 was cancelled late in the review over bioanalytical method validation questions, and on December 1, 2015 FDA issued a complete response letter stating that the Phase III design was no longer adequate to demonstrate clinical benefit, raising concerns about entry criteria, dose titration and bioanalytical method validation, and asking for at least one additional Phase III study. No resubmission followed
- EMA: Repros reported submitting a centralized marketing authorization application for enclomiphene on September 12, 2016; the EMA lists the applicant as Renable Pharma Limited and the product as EnCyzix. The CHMP adopted a negative opinion on 25 January 2018 and the application was formally refused on 6 April 2018: the studies showed higher testosterone but did not assess whether symptoms such as bone strength, body weight or sexual function improved, and the committee noted a risk of venous thromboembolism
- After 2018: Allergan announced its acquisition of Repros in December 2017 and the enclomiphene program was not continued; later pipeline listings record development as discontinued. As of October 2026, ClinicalTrials.gov lists no recruiting or active enclomiphene trial; a Baylor male-infertility study (NCT02160704) was withdrawn without enrolling, and the Repros Phase II metabolic study ZA-205 (NCT02651688, 50 men) completed in May 2017 with results posted to the registry in June 2019 and no development afterward
- Later evidence is secondary: a 2025 meta-analysis pooling clomiphene and enclomiphene RCTs found SERMs raised total testosterone by roughly 274 ng/dL versus placebo with no significant difference versus testosterone gel (Hohl et al., Archives of Endocrinology and Metabolism, 2025;69(5):e250093), and the British Society of Sexual Medicine published a position statement on its potential use (Foster et al., World Journal of Men’s Health, 2026;44(3):480–3). No trial has shown a symptomatic or hard-outcome benefit
Common dosage forms
In the United States enclomiphene citrate is dispensed as compounded oral capsules, and sometimes tablets, through 503A compounding pharmacies, usually via telehealth prescriptions; bulk enclomiphene citrate powder is listed in the NDC directory as a compounding ingredient. Sublingual troche formulations have appeared more recently in clinic case series. Research-chemical vendors list it as an oral solution in dropper bottles, as tablets or capsules, or as bulk powder, almost always as the citrate salt. Unlike most compounds in the research-peptide market, it is not an injectable or a lyophilized vial product. No FDA-approved finished product exists in any form.
Key considerations
- Not an approved drug anywhere. FDA issued a complete response letter in 2015 and the EMA refused the MAA in 2018; the Research Market status reflects that no US approval exists and no development aimed at approval is active. US compounding continues only because enclomiphene citrate sits in Category 1 (“under evaluation”) of FDA’s list of substances nominated for 503A compounding (updated May 14, 2026), where FDA exercises enforcement discretion pending a decision. That is not the 503A Bulks List: at the June 8, 2022 Pharmacy Compounding Advisory Committee, FDA proposed that enclomiphene citrate not be listed and the committee voted 8–4 against listing (4 yes, 8 no, 0 abstain), citing lack of clinical efficacy evidence; no final rule has followed. Clomiphene’s approval covers the isomer mixture, not the isolated trans-isomer
- The evidence gap is the one both regulators named. Phase III endpoints were restricted to testosterone, gonadotropin and sperm-concentration numbers in overweight men with secondary hypogonadism; no study measured symptoms, bone, fertility outcomes or long-term safety, and the one metabolic study (ZA-205) was a 50-man Phase II that never led anywhere
- Safety signals in the literature: venous thromboembolism risk flagged by the CHMP (a class concern for SERMs); LH and FSH pushed above the normal range and a larger IGF-1 decrease than with testosterone gel in Phase II (Wiehle et al., 2013); clomiphene-class visual and mood effects documented for the mixture; and isolated case reports such as new-onset atrial flutter after dose escalation in a man with prior mitral valve repair (Tariq et al., Cureus, 2026;18(8):e114562). Compounded and research-market products carry no FDA review of potency or purity
- Naming confusions: enclomiphene is not clomiphene (Clomid), which is a fixed enclomiphene/zuclomiphene mixture; “enclomifene” is the INN spelling used by the EMA; Androxal and EnCyzix were proposed brand names that never reached market. It is a small-molecule SERM, not a peptide and not an anabolic steroid, despite being sold in “post-cycle” and “testosterone restoration” bundles alongside peptides; no trial has measured lean mass or strength as an endpoint