Enclomiphene Side Effects: Trial Data, Clots and User Reports

Most men who take enclomiphene in studies report no side effects, but a meaningful minority do. The best single number comes from the two phase III trials published by Kim and colleagues in BJU International in 2016: 53 men (21%) had side effects that investigators judged possibly, probably or definitely related to the drug, and none of these events were severe or serious.

Smaller studies give lower figures. A 2024 retrospective study in Translational Andrology and Urology by Saffati and colleagues followed 66 men and found any side effect in 13.8% of those on enclomiphene, compared with 47% of men on clomiphene. A 2026 position statement from the British Society for Sexual Medicine (BSSM) lists the individual events with the rates below.

The BSSM statement does not name the primary source for these percentages, so treat them as the society's summary rather than a single trial result. What they show is consistent with the trials: the common enclomiphene side effects are mild and reversible, and they are less frequent than with Clomid. This page covers the trial record, the blood clot question, vision, and what men report on forums. For background on the drug itself, start with what enclomiphene is.

The trial reports describe a short list of problems. In the phase IIB trial by Wiehle and colleagues (Fertility and Sterility, 2014), four men stopped treatment because of mild to moderate adverse events, all of them on the higher 25 mg dose. The paper describes mild hives (judged probably unrelated to the drug), inability to climax with loss of sensation, and mild nausea with dry heaving.

The earlier phase II study by Wiehle (BJU International, 2013) looked at a wider set of lab values over 6 weeks. The drug had no significant effect on thyroid hormone, adrenal hormones, cortisol, blood lipids or bone markers. Both enclomiphene and testosterone gel lowered IGF-1, and the drop was larger with enclomiphene. The same study noted that LH and FSH rose "above the normal range", which is the intended effect taken further than the body normally goes.

Estradiol is the other value to watch. Because the testes make more testosterone, some of it converts to estradiol. The Saffati study found estradiol fell slightly on enclomiphene (by about 6 pg/mL on average) but rose by 17.5 pg/mL on clomiphene. Individual men can still see higher estradiol, which is behind the nipple sensitivity some describe.

The trials lasted between 6 weeks and 6 months. They cannot tell us about effects that appear after years of use, and no long-term enclomiphene side effects study exists yet.

The most serious concern about enclomiphene comes from Europe. On 25 January 2018 the European Medicines Agency refused approval for EnCyzix, an enclomifene capsule. Its published summary gives two reasons. The first was that the studies did not show whether men's symptoms improved. The second was that "there is a risk of venous thromboembolism", meaning clots in the veins such as deep vein thrombosis.

The EMA document does not give a rate, and the phase III paper by Kim does not report clot events. So the risk is a regulator's judgement, not a measured percentage. The closest official reference point is Clomid: its label lists thromboembolism among the reported complications of severe ovarian hyperstimulation in women.

In practice, men with a history of deep vein thrombosis, pulmonary embolism or a clotting disorder should raise this with a doctor before starting. Sudden leg swelling or pain, chest pain or sudden shortness of breath on any estrogen receptor drug needs urgent medical care, not a wait-and-see approach.

Vision problems are the best known risk of Clomid. Its FDA label warns that blurring, spots or flashes may occur and that "the visual disturbances may be irreversible, especially with increased dosage or duration of therapy". In women, visual symptoms were reported in 1.5% of patients.

For enclomiphene, no trial we reviewed reported a visual side effect rate. The phase III trials did include a baseline eye exam, which shows the investigators took the risk seriously. Because enclomiphene is part of clomiphene, most doctors apply the same caution.

Forum reports on this are few. On ExcelMale, one user described eye floaters from day 2 on 12.5 mg daily, and another said his floaters "seem to be worse than ever" at 6 weeks before later calling it a "coincidence". A long-term user on the same forum reported nearly two years of use "without incident". These are individual accounts, not data. Any new blurring, flashing lights or shadows in vision should mean stopping and seeing an eye doctor. Our Clomid side effects page covers the visual warning in more detail.

Blood tests are not the whole story, and forums show a pattern the trials did not measure. The following themes come up across several users on ExcelMale, MESO-Rx and AnabolicMinds. They are personal reports, not confirmed by studies.

The low libido pattern matches the Saffati data, where 8.6% of men on enclomiphene reported decreased libido (33.3% on clomiphene). The enclomiphene results article collects the lab numbers men post.

Against Clomid, the evidence favors enclomiphene. In the Saffati comparison, decreased libido was 8.6% vs 33.3%, reduced energy 5.2% vs 16.7%, mood changes 0% vs 9.1%, and gynecomastia 0% vs 3%. The likely reason is zuclomiphene, the long-acting isomer in Clomid that enclomiphene leaves out. See enclomiphene vs Clomid for the full comparison.

Against testosterone replacement, the trade-offs are different. Testosterone therapy suppresses sperm production and often raises red blood cell counts. For clomiphene, a 2017 study by Wheeler and colleagues (Journal of Urology) found polycythemia in 1.7% of 188 men compared with 11.2% of 175 men on testosterone. No equivalent study exists for enclomiphene alone, but it works by the same route.

Sensible monitoring on any of these drugs includes total testosterone, estradiol, LH and FSH at about 4 weeks, a blood count, and prompt reporting of any vision change or clot symptom. Details on doses are in the enclomiphene dosage guide.

Clomid.org is an independent educational resource. We are not affiliated with any pharmaceutical manufacturer, compounding pharmacy, telehealth company or healthcare provider. This content is for informational purposes only and does not constitute medical advice. Images on this site are illustrative artwork made for editorial purposes; they do not show real products, packaging or labels and are not an advertisement or an offer to sell.