Last updated 25 August 2026.
Enclomiphene is not an FDA-approved drug. It is available as a compounded medication, prepared by a licensed pharmacy for an individual patient on the prescription of a licensed clinician. Compounded medications are not reviewed by FDA for safety, effectiveness or quality before being dispensed. This page is educational. It is not medical advice, and whether any treatment is appropriate for a particular person is a decision for a state-licensed clinician.
The short version: the theory behind separating enclomiphene from clomiphene is sound and well documented. The evidence that it produces a better outcome in practice is thin. Both of those things are true at once, and most comparisons only tell you the first.
The chemistry, which is not disputed
Clomiphene citrate is a mixture of two geometric isomers. The FDA-approved labelling for clomiphene describes it as containing between 30% and 50% of the cis isomer, zuclomiphene, with the rest being the trans isomer, enclomiphene.
The two behave differently, and close to oppositely:
| Enclomiphene, the trans isomer | Zuclomiphene, the cis isomer | |
|---|---|---|
| Estrogen receptor activity | Antiestrogenic | Partly agonist, partly antagonist |
| Half-life | Short, in the order of hours | Long, in the order of a day |
| Accumulation | Clears quickly | Persists. Detectable in serum weeks later and in urine for months |
| Proportion of clomiphene | Roughly half to two thirds | 30% to 50%, and variable |
So taking clomiphene means taking a variable mixture in which the long-lived component has partly opposite pharmacology to the short-lived one. Isolating enclomiphene gives you cleaner and more predictable pharmacology. That much is real and documented.
Where the evidence stops
This is the part usually left out.
- There is no randomised head-to-head trial of enclomiphene against clomiphene in men. None. The comparison everyone makes has never been run properly.
- The only direct comparison is a retrospective chart review of 46 men on enclomiphene and 32 on clomiphene at a single institution. Both raised testosterone. Enclomiphene raised gonadotropins and motile sperm count more, though the clomiphene group’s changes did not reach statistical significance in a sample that size. The authors themselves list selection bias, confounded baselines, and no long-term follow-up among the limitations.
- No study attributes any specific clinical side effect to zuclomiphene. The idea that zuclomiphene is responsible for clomiphene’s side effects is a mechanistic hypothesis. We could find no clinical comparison testing it.
Every confident claim we could find that enclomiphene causes fewer side effects than clomiphene traced back to a compounding pharmacy or a telehealth marketing page, not to a study.
The comparison that goes the other way
Worth knowing, because it is rarely mentioned by anyone selling enclomiphene.
- Clomiphene has the longer human track record in men, and more randomised trials. In the 2025 meta-analysis of this drug class, six of the ten included trials used clomiphene, and both of the two longest trials, at 30 weeks, were clomiphene trials.
- Clomiphene has an FDA-approved product and therefore a label, with a documented safety section. Enclomiphene has neither.
- Enclomiphene was submitted to FDA and not approved. It received a Complete Response Letter in December 2015.
Neither is FDA-approved for use in men. Clomiphene is approved for ovulatory dysfunction in women, and its own labelling states there are no adequate or well-controlled studies demonstrating effectiveness in the treatment of male infertility. Use in men is off-label for one and unapproved for the other.
Side by side
| Enclomiphene | Clomiphene | |
|---|---|---|
| What it is | One isolated isomer | A mixture of both isomers |
| Pharmacology | Antiestrogenic only | Mixed, and variable between batches |
| FDA-approved product | No | Yes, but for ovulatory dysfunction in women |
| Approved for use in men | No | No |
| Randomised trials in men | 4, roughly 191 men, longest adequately powered trial 16 weeks | 6 in the 2025 meta-analysis, including both 30-week trials |
| Head-to-head against each other | None | None |
| 503A compounding status | Category 1 | Not on the Category 1 list |
| Long-term safety data | None published | Limited |
So which is better?
On the available evidence, that question does not have a defensible answer, and we would rather say so than manufacture one.
What can be said fairly: enclomiphene is the purified antiestrogenic isomer, which gives it cleaner and more predictable pharmacology and avoids the long-accumulating estrogenic fraction. Whether that translates into fewer side effects or better outcomes in men has not been tested in a randomised trial. Anyone stating otherwise is extrapolating from mechanism, which is a reasonable thing for a clinician to do when choosing between options and an unreasonable thing for a seller to present as established fact.
Related
- Enclomiphene: what it is and what the research shows
- Enclomiphene side effects
- Every treatment we offer, with prices
References
- Kim ED, McCullough A, Kaminetsky J. Oral enclomiphene citrate raises testosterone and preserves sperm counts in obese hypogonadal men, unlike topical testosterone. BJU Int. 2016;117(4):677-685. PMID 26496621
- Wiehle RD, Fontenot GK, Wike J, et al. Enclomiphene citrate stimulates testosterone production while preventing oligospermia: a randomized phase II clinical trial comparing topical testosterone. Fertil Steril. 2014;102(3):720-727.
- Wiehle R, Cunningham GR, Pitteloud N, et al. Testosterone restoration using enclomiphene citrate in men with secondary hypogonadism. BJU Int. 2013;112(8):1188-1200. PMID 23875626
- Kaminetsky J, Werner M, Fontenot G, Wiehle RD. Oral enclomiphene citrate stimulates the endogenous production of testosterone and sperm counts in men with low testosterone. J Sex Med. 2013;10(6):1628-1635. PMID 23530575
- Hohl A, Chavez MP, Pasqualotto E, et al. 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):e250093. PMC12510335
- Repros Therapeutics. Receipt of Complete Response Letter from FDA for enclomiphene, 1 December 2015.
- FDA. Bulk drug substances nominated for use in compounding under section 503A, updated 14 May 2026.
If you are weighing the two, what we dispense is Enclomiphene, prescribed after an intake by a licensed clinician.
General educational information about medications. Not medical advice, not a recommendation to take anything, and not a claim about the effectiveness or safety of either. Prescription decisions are made by state-licensed clinicians.
