Enclomiphene Citrate Pharmacogenomics and Genetic Variability

Is there pharmacogenomic data on enclomiphene?

Pharmacogenomics asks whether inherited differences in drug-metabolizing enzymes or in the drug's receptor change blood levels or response. The genotype work that exists is on clomiphene citrate, the mixture of enclomiphene and zuclomiphene. A 2012 study correlating CYP2D6 genotype in 30 human liver donors with clomiphene metabolite formation observed a strong gene-dose effect [11]. That result is about the mixture, and enclomiphene is not simply clomiphene [1].

For enclomiphene itself, no label gives a genotype-based dose [1][2]. The trials compared enclomiphene with testosterone gel or placebo and reported hormone levels and sperm counts [4][5].

How the body handles enclomiphene

Oral enclomiphene is absorbed rapidly, peaks 2 to 3 hours after a dose, has a half-life of about 10 hours, forms 4-hydroxy enclomiphene as its main metabolite and is excreted mainly in feces [1]. It blocks pituitary estrogen receptors, so the pituitary releases more LH and FSH, signalling the testes to make more testosterone [1].

Enclomiphene is one isomer of clomiphene citrate; per FDA, the USP monograph gives enclomiphene content of clomiphene as 50 to 70 percent [1], and enclomiphene is the more anti-estrogenic, pro-gonadotropic isomer [6].

Why no label gives genotype-guided dosing

FDA's 2022 advisory committee materials state that no FDA-approved drugs contain enclomiphene as an active ingredient [1]. The EMA committee adopted a negative opinion on 25 January 2018 recommending refusal of marketing authorisation for EnCyzix (enclomifene), based on 4 main studies in 588 patients [2]. Enclomiphene citrate sits in Category 1 of FDA's bulk drug substance list, under evaluation, as of the list updated 14 May 2026 [7].

Response and side effects in the trials

In a 12-week phase 3 trial, 78.8 percent of men on enclomiphene reached an average 24-hour testosterone of 300 to 1040 ng/dL (95% CI 70.3 to 85.3) [8]; in a second trial of the same design, 81.3 percent did (95% CI 73.9 to 87.0) [9].

The most frequent side effects were headache, hot flushes, nausea and muscle spasm, and reasons for stopping included blurred vision and aggression; in one 12-week trial headache occurred in 7 of 112 men on 12.5 mg versus 1 of 47 on placebo [9]. FDA listed cardiac and thromboembolic events, raised estradiol, PSA and hematocrit, and no long-term safety data [1]. The Clomid label covers the clomiphene mixture, not enclomiphene alone; the label says visual disturbances are usually reversible but may be irreversible, especially with increased dosage or duration of therapy [10].

The practical answer

There is no enclomiphene-specific genotype guidance to apply. Doses with data behind them are 6.25, 12.5 and 25 mg daily for 6 weeks in a phase 2 trial [3], and 12.5 mg daily titrated to 25 mg at week 6 in the phase 3 protocols [8].

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