Enclomiphene Side Effects: What Trials and Regulators Found

In placebo-controlled trials, most reported enclomiphene side effects were mild, and published lists put headache and hot flushes among the most common. Overall adverse-event rates were not clearly higher than placebo (Arch Endocrinol Metab, 2025). Those trials lasted only weeks to months, though. Regulators were more cautious. Neither the FDA nor European regulators have approved enclomiphene, and long-term safety data is absent (BSSM, World J Mens Health, 2026).

Key takeaways

• Placebo-controlled enclomiphene trials recorded mostly mild side effects and no clear excess over placebo, but the trials cited here followed men for only a few months.
• Raised hematocrit and vision changes sit at different evidence levels: one is a single trial discontinuation, and the other is a warning inherited from clomiphene's label that regulators asked to monitor.
• Enclomiphene is not an FDA-approved medication, and compounded medications are not FDA-approved.
• The open safety questions are why enclomiphene use calls for clinician oversight with a live visit and lab work.

Why do enclomiphene side-effect numbers differ so much online?

The numbers differ because websites blend three kinds of evidence and count adverse events in different ways. Once you know which kind of evidence a claim comes from, most of the contradictions disappear.

Most common safety claims about enclomiphene fall into one of three tiers:

1. Tier 1, trial data. These are events recorded in randomized, placebo-controlled trials, meaning studies where some men got a dummy pill for comparison.
2. Tier 2, regulator and professional-society conclusions. These are judgments by the FDA, the European Medicines Agency (EMA) and the British Society for Sexual Medicine (BSSM) after reviewing the data.
3. Tier 3, carried-over warnings. These are concerns copied from clomiphene's FDA label or from testosterone replacement therapy (TRT). They are plausible, but they have not been shown for enclomiphene itself.

Four counting and sourcing choices also change the numbers you see.

• Reporting thresholds. Trial registries often list only events above a set frequency. The phase III registry entry NCT01532414 reported "other" adverse events at a 3% threshold, so rarer events never appear in that table (ClinicalTrials.gov NCT01532414).
• Related versus all events. Some reports count every adverse event. Others count only events judged possibly, probably or definitely related to the drug. One trial in a 2025 meta-analysis reported a related-event rate of about 21%, with none severe (Arch Endocrinol Metab, 2025).
• Study design. A retrospective chart review looks back at existing records and is weaker evidence than a randomized trial. Its rates should not be quoted as if they were trial rates.
• Unsourced figures. Some pages quote side-effect rates with no traceable primary source. If a number has no traceable source, treat it as noise.

What enclomiphene side effects showed up in clinical trials?

The main phase III registry data recorded no serious adverse events in any arm, including placebo. Published lists put individual symptoms, such as headache, at low single-digit rates. The catch is that follow-up was short.

The phase III registry results for NCT01532414 look like this (ClinicalTrials.gov NCT01532414):

Adverse events were tracked for 13 to 18 weeks, depending on whether a participant's dose was adjusted, plus one week of follow-up. The higher-dose arm had only 21 men, so its higher percentage rests on six people.

Other trial data point the same way:

• The 2025 meta-analysis. A meta-analysis pools results from several trials. This one, covering randomized trials of clomiphene or enclomiphene, found no significant difference in adverse-event frequency among SERM, testosterone gel and placebo groups. A SERM is a selective estrogen receptor modulator, the drug class enclomiphene belongs to. In one included enclomiphene study, there were no serious adverse events and no significant chemistry, blood count or urinalysis changes attributed to the drug (Arch Endocrinol Metab, 2025).
• The Wiehle trial. As summarized in the same review, adverse events were similar across the SERM, testosterone gel and placebo arms. The reported SERM-group events included one mildly elevated estradiol and headaches.
• The BSSM summary. The BSSM lists headache at 1.6%, hot flushes at 1.1%, nausea at 1.0%, muscle spasms at 0.9% and dizziness at 0.7% (BSSM, World J Mens Health, 2026).

It also matters what these trials were built to measure. The pooled ZA-304 and ZA-305 phase III studies were double-blind and placebo-controlled. They enrolled overweight men with secondary hypogonadism, which means low testosterone caused by weak signaling from the brain rather than a testicular problem. Active dosing lasted up to 16 weeks, and 256 men completed the trials (BJU Int, 2015). Trials of that size and length can pick up common side effects. They cannot detect rare ones.

Are there serious risks like hematocrit, vision changes or blood clots?

Possibly, but the evidence behind each concern is different. None of them has a reliable trial-measured rate for enclomiphene.

Hematocrit is the share of your blood made up of red blood cells. In the meta-analysis, one of two discontinuations in a higher-dose enclomiphene group was due to elevated hematocrit (Arch Endocrinol Metab, 2025). That single event is a reason blood counts are among the markers a clinician may track.

Vision changes are a concern borrowed from clomiphene. Clomiphene's FDA label warns of blurring, spots or flashes that become more common with higher total dose or longer use. These are usually reversible, but prolonged and possibly irreversible cases have been reported (Clomid label, FDA, 2017). For enclomiphene specifically, the EMA found no conclusive evidence of new or progressing cataracts, but it recommended ocular safety monitoring to collect more data (FDA advisory committee materials).

Mood changes and PSA also come from other drugs. Clomiphene's label lists anxiety, irritability and mood changes among postmarketing reports (Clomid label, FDA, 2017). Rises in prostate-specific antigen (PSA), a prostate blood marker, are associated with TRT (Arch Endocrinol Metab, 2025). The verified sources do not show that enclomiphene raised PSA.

Venous thromboembolism (VTE) means a blood clot in a vein, which can travel to the lungs. None of the verified sources reports a clot signal or a regulator clot finding for enclomiphene. The trials were too small and short to detect rare events, so neither "causes blood clots" nor "no clot risk" is supported by this evidence.

Sudden leg swelling, chest pain, shortness of breath or sudden vision loss is an emergency. Call 911. Telehealth is not for emergencies.

Enclomiphene vs clomiphene side effects: what's different?

Enclomiphene is one component of clomiphene, and early data suggest it causes fewer side effects. That evidence comes from a single retrospective study, not a randomized trial.

Clomiphene is a mix of two isomers, which are versions of the same molecule with the same atoms arranged differently. Enclomiphene is the trans-isomer and is the more anti-estrogenic of the two. Zuclomiphene, the other isomer, acts more like estrogen (BSSM, World J Mens Health, 2026). Removing zuclomiphene is the theoretical basis for a cleaner side-effect profile.

The main comparison is a single-center retrospective study of 66 men who took clomiphene and later switched to enclomiphene (Transl Androl Urol, 2024):

• Adverse effects were reported in 13.8% of men on enclomiphene and 47% on clomiphene.
• Decreased libido was reported in 8.6% on enclomiphene and 33.3% on clomiphene.
• Reduced energy and mood changes were significantly less frequent on enclomiphene.
• Estradiol fell by 5.92 pg/mL on enclomiphene and rose by 17.50 pg/mL on clomiphene.

This study has real limits. Every patient had already tried clomiphene. Patients switched for different reasons, which the authors acknowledge introduces bias. The study also came from one center, and the authors call for larger long-term studies. Clomiphene's own FDA label is written for ovulation induction in women, so its warnings were never built around men using it off-label (Clomid label, FDA, 2017).

Why is enclomiphene not FDA-approved?

Enclomiphene is not FDA-approved because its development stalled at the regulatory stage: the FDA issued a Complete Response, the EMA recommended refusal, and the manufacturer stopped development in 2021. That same history is why long-term safety data is so thin.

• Short trials. The pivotal studies ran weeks to a few months (BJU Int, 2015).
• The FDA Complete Response. A Complete Response Letter is the FDA's notice that an application cannot be approved as submitted. In December 2015 the sponsor announced one stating that the phase 3 design was no longer adequate to demonstrate clinical benefit. The FDA also raised concerns about entry criteria, dose titration and validation of the lab methods (FDA advisory committee materials).
• The EMA refusal. In 2018 the EMA recommended refusal. It also considered the data incomplete for adjusting use in older adults, in poor CYP2D6 metabolizers (people whose bodies break down certain drugs slowly because of a liver enzyme variant) and in people with kidney or liver impairment (FDA advisory committee materials).
• Development stopped. The manufacturer discontinued development in 2021 (BSSM, World J Mens Health, 2026).

The BSSM position statement is cautious (BSSM, World J Mens Health, 2026). Because long-term efficacy and safety data are missing, it advises limiting use to experienced clinicians in specialist or research settings, with proper patient counselling. It also notes enclomiphene may be available off-label through compounding pharmacies.

Enclomiphene has been nominated for the list of bulk drug substances that can be used in compounding under section 503A (FDA advisory committee materials). A nomination or evaluation is not approval, and it is not an FDA endorsement. Compounded medications are not FDA-approved. They are prepared by state-licensed 503A compounding pharmacies or FDA-registered 503B outsourcing facilities. For more on what that means, read the compounding disclosure and the explainer on compounded vs. branded medications.

What does enclomiphene monitoring involve?

Monitoring means lab work and clinician check-ins to watch the markers the trials tracked. Which labs to order, how often, and whether to continue are clinical decisions.

Enclomiphene blocks estrogen receptors in the pituitary gland. That raises LH and FSH, the hormones that signal the testes to make testosterone and sperm (BSSM, World J Mens Health, 2026). Because it works through the body's own signaling, the markers studied in trials are the kinds a clinician may review:

• total testosterone, LH and FSH
• estradiol
• hematocrit and other blood counts
• general blood chemistry

The EMA's eye-safety recommendation adds vision questions to that picture. Medical history matters too. Past blood clots, eye conditions, and liver or kidney problems are the kind of history a licensed clinician weighs. The EMA judged pharmacokinetic data incomplete for people with kidney or liver impairment (FDA advisory committee materials), and clomiphene's label lists liver disease as a contraindication (Clomid label, FDA, 2017).

Report any vision change, mood change or new symptom to your clinician. Follow your clinician's guidance and pharmacy instructions.

How access works through New Blue

New Blue is a technology and administrative services platform. Medical services are provided by independent licensed clinicians; medications are dispensed only if prescribed.

Enclomiphene hormone support is a synchronous pathway, meaning it requires a live clinician visit plus lab work. It is never an asynchronous form.

1. You complete an intake covering your health history.
2. You complete lab work and a live visit with a licensed clinician.
3. The clinician decides whether enclomiphene is appropriate.
4. If prescribed, a licensed partner pharmacy ships the medication directly to you.

Not everyone qualifies. Eligibility depends on your intake, labs and live clinical review, and that's how it should work. The pathway is for adults 21 and older. Consultation timing varies by clinician availability. Availability varies by state, so check state availability. For current pricing and details, see the enclomiphene hormone support page. For the broader comparison, read enclomiphene vs. testosterone replacement, and for sperm and recovery context, see does TRT affect fertility.

Frequently Asked Questions

What is the most common enclomiphene side effect?

Headache and hot flushes appear most often in published lists. The BSSM summary puts them at 1.6% and 1.1%. Long-term safety data are absent, so those figures say little about long-term use.

Does enclomiphene cause blood clots?

The verified sources report no measured clot rate for enclomiphene. The trials were too small and too short to detect rare events like blood clots, so the evidence neither confirms nor rules out a risk. A history of clots is something a clinician needs to know before any decision is made.

Can enclomiphene affect vision?

Vision changes are a known warning on clomiphene's FDA label and are carried over as a concern for enclomiphene. The EMA found no conclusive evidence of cataracts with enclomiphene but recommended eye-safety monitoring. Report any blurring, spots or flashes promptly, and call 911 for sudden vision loss.

Is enclomiphene safer than clomiphene?

One retrospective study of 66 men found fewer side effects after switching from clomiphene to enclomiphene. That study had selection bias and no randomization. No head-to-head randomized trial appears in the verified evidence.

Does enclomiphene affect sperm production?

In the pooled ZA-304 and ZA-305 phase III trials, enclomiphene maintained sperm concentrations, while testosterone gel groups showed significant decreases from baseline. Enclomiphene works by raising LH and FSH, which signal the testes to make testosterone and sperm. Whether it fits a particular man's fertility goals is a clinical decision.

Do I need labs to use enclomiphene?

Labs are central to clinician oversight because trials tracked hormone levels, blood counts and chemistry. At New Blue, every hormone pathway, including enclomiphene hormone support, requires a live clinician visit plus lab work. Which labs and how often is a clinical decision.

Sources

1. British Society of Sexual Medicine: Position Statement for the Potential Use of Enclomiphene in the Treatment of Male Hypogonadism. The World Journal of Men's Health, 2026. https://doi.org/10.5534/wjmh.250395
2. Clomiphene or enclomiphene citrate for the treatment of male hypogonadism: a systematic review and meta-analysis of randomized controlled trials. Archives of Endocrinology and Metabolism, 2025. https://pubmed.ncbi.nlm.nih.gov/41066380/
3. Enclomiphene citrate evaluation (Pharmacy Compounding Advisory Committee materials). U.S. Food and Drug Administration, date not listed. https://www.fda.gov/media/159042/download
4. Phase III Study to Evaluated Morning Testosterone Normalization in Men With Secondary Hypogonadism (NCT01532414). ClinicalTrials.gov, 2014. https://clinicaltrials.gov/study/NCT01532414
5. Oral enclomiphene citrate raises testosterone and preserves sperm counts in obese hypogonadal men, unlike topical testosterone: restoration instead of replacement. BJU International, 2015. https://doi.org/10.1111/bju.13337
6. Safety and efficacy of enclomiphene and clomiphene for hypogonadal men. Translational Andrology and Urology, 2024. https://doi.org/10.21037/tau-24-238
7. CLOMID (clomiphene citrate tablets USP) prescribing information. U.S. Food and Drug Administration, 2017. https://www.accessdata.fda.gov/drugsatfda_docs/label/2017/016131s028lbl.pdf

Medical disclaimer: This article is for educational purposes only and is not medical advice. Treatment decisions, including whether any medication is appropriate, are made by a licensed clinician based on your history, labs and clinical review. New Blue Health is a technology and administrative services platform, not a medical provider.