Overview
Enclomiphene citrate is the pharmacologically active trans-isomer of clomiphene citrate (Clomid), a medication that has been used for decades in reproductive medicine. While clomiphene contains both the trans (enclomiphene) and cis (zuclomiphene) isomers, enclomiphene alone provides the desired anti-estrogenic effects at the hypothalamus without the prolonged estrogenic activity of zuclomiphene, which has a much longer half-life.
Developed by Repros Therapeutics under the brand name Androxal, enclomiphene was studied extensively in Phase 3 clinical trials for secondary hypogonadism in overweight men with low testosterone. Unlike exogenous testosterone replacement therapy (TRT), enclomiphene stimulates endogenous testosterone production by blocking estrogen negative feedback at the hypothalamus, thereby increasing LH and FSH secretion from the pituitary gland.
The critical advantage of enclomiphene over TRT is the preservation of spermatogenesis. Exogenous testosterone suppresses the hypothalamic-pituitary-gonadal (HPG) axis, leading to testicular atrophy and infertility—a significant concern for younger men. Enclomiphene, by stimulating the HPG axis, actually supports sperm production while normalizing testosterone levels.
Although the FDA did not approve enclomiphene due to manufacturing concerns (not efficacy or safety issues), it remains available through compounding pharmacies and has generated substantial clinical evidence supporting its use in male hypogonadism. This guide reviews the clinical data, pharmacology, and practical considerations.
Quick facts
- Mechanism
- Selective estrogen receptor modulator restoring endogenous testosterone
- Primary use
- Testosterone Restoration & Fertility Preservation
- Evidence
- strong
- FDA
- Not approved
- Route
- Oral administration
- Typical results
- Testosterone normalization within 2–4 weeks; maintained fertility
Chemical information
Enclomiphene citrate has a molecular mass of 598.09 g/mol (citrate salt) with the base compound formula C₂₆H₂₈ClNO₃. It is the trans-isomer of clomiphene, featuring a triphenylethylene core with a chlorine substituent and a diethylaminoethoxy side chain. The trans configuration is critical for its predominantly anti-estrogenic pharmacological profile at the hypothalamus.
How Enclomiphene works
Enclomiphene functions as a selective estrogen receptor modulator (SERM) that primarily antagonizes estrogen receptors in the hypothalamus. Under normal physiology, estradiol (converted from testosterone via aromatase) provides negative feedback to the hypothalamus, suppressing GnRH pulse frequency and amplitude. By blocking this feedback loop, enclomiphene 'tricks' the hypothalamus into perceiving low estrogen levels.
This hypothalamic estrogen receptor blockade results in increased GnRH pulse frequency, which stimulates the anterior pituitary to release more luteinizing hormone (LH) and follicle-stimulating hormone (FSH). LH acts on Leydig cells in the testes to produce testosterone, while FSH supports Sertoli cells and spermatogenesis. This dual stimulation is the key differentiator from exogenous testosterone.
Unlike zuclomiphene (the cis-isomer found in standard clomiphene), enclomiphene has a shorter half-life and does not accumulate to produce prolonged estrogenic effects. Zuclomiphene's long half-life (weeks to months) can lead to paradoxical estrogenic symptoms including mood disturbances, visual changes, and gynecomastia—side effects commonly attributed to clomiphene therapy that are largely absent with pure enclomiphene.
Clinical trials demonstrated that enclomiphene 12.5–25 mg daily consistently raised total testosterone from hypogonadal levels (<300 ng/dL) to the normal range (450–600+ ng/dL) while maintaining or improving sperm concentration. In contrast, testosterone gel therapy in the same trials significantly reduced sperm counts.
- Hypothalamic ER antagonism: Blocks estrogen receptors in the hypothalamus to disinhibit GnRH secretion
- LH/FSH elevation: Increases pituitary gonadotropin output, driving testicular testosterone production
- Spermatogenesis preservation: FSH stimulation supports Sertoli cell function and sperm maturation
- Short half-life advantage: Unlike zuclomiphene, does not accumulate or cause prolonged estrogenic effects
- Selective tissue action: Anti-estrogenic in hypothalamus while not significantly affecting bone or cardiovascular estrogen signaling
- HPG axis restoration: Normalizes the entire hormonal cascade rather than bypassing it
Pharmacokinetics
Pharmacokinetic data is available from multiple Phase 1–3 clinical trials in men with secondary hypogonadism.
| Parameter | Value | Significance |
|---|---|---|
| Bioavailability (Oral) | Well absorbed; high oral bioavailability | Convenient once-daily oral dosing |
| Half-life | ~10 hours | Much shorter than zuclomiphene (weeks); no accumulation |
| Tmax | 1.5–3 hours | Rapid absorption with moderate food effect |
| Protein binding | >95% | Highly protein-bound in circulation |
| Metabolism | Hepatic (CYP2D6, CYP3A4) | Standard hepatic metabolism; minimal active metabolites |
| Steady state | Achieved within 5–7 days | Testosterone response begins within 1–2 weeks |
Dosing & administration
In Phase 3 clinical trials, enclomiphene was studied at doses of 12.5 mg and 25 mg taken once daily. The 12.5 mg dose was effective for most men in normalizing testosterone to the 450–550 ng/dL range, while the 25 mg dose provided slightly higher levels. Most clinicians start at 12.5 mg and titrate based on lab work obtained at 4–6 weeks.
The medication is taken orally, typically in the morning, with or without food. Unlike TRT, enclomiphene does not require injection training, topical application, or concern about transference to partners or children. Treatment is ongoing; testosterone levels return to baseline within 2–3 weeks of discontinuation.
Monitoring should include total testosterone, free testosterone, LH, FSH, estradiol, hematocrit, and PSA at baseline and every 3–6 months. Sperm analysis should be performed for men specifically concerned about fertility.
Important: These dosing ranges are not FDA-approved. Any use should be under qualified medical supervision.
Side effects & safety
Enclomiphene demonstrated a favorable safety profile across multiple Phase 3 trials involving over 800 men treated for up to 2 years. The most common reason for the FDA's complete response letter was manufacturing-related concerns, not safety or efficacy issues. Compared to standard clomiphene, enclomiphene shows fewer estrogenic side effects due to the absence of zuclomiphene accumulation.
Common
- • Headache (8–10%)
- • Hot flashes (5–7%)
- • Mild nausea
- • Upper respiratory tract infection
- • Fatigue
- • Mild mood changes during initial titration
Serious / potential risks
- • Visual disturbances (rare, more associated with zuclomiphene)
- • Overstimulation of testosterone production (rare)
- • Theoretical risk of venous thromboembolism (class effect of SERMs)
- • Potential hepatic effects with long-term use
- • Polycythemia if testosterone levels rise significantly
Drug interactions
Enclomiphene is metabolized primarily by CYP2D6 and CYP3A4, creating potential for drug interactions.
| Medication | Interaction | Recommendation |
|---|---|---|
| CYP2D6 inhibitors (Fluoxetine, Paroxetine) | May increase enclomiphene levels | Monitor for enhanced effects; consider dose reduction |
| CYP3A4 inhibitors (Ketoconazole, Clarithromycin) | May increase enclomiphene exposure | Use with caution; monitor testosterone levels |
| Aromatase inhibitors (Anastrozole) | Both reduce estrogen signaling; additive effect | Generally not combined; may cause excessive estrogen suppression |
| Exogenous testosterone | TRT suppresses HPG axis, opposing enclomiphene mechanism | Contradictory mechanisms; do not use together |
| Anticoagulants | SERMs may have minor effects on coagulation | Monitor INR if on warfarin; low clinical significance |
Storage & handling
Oral Capsules/Tablets
- • Store at room temperature (20–25°C / 68–77°F)
- • Protect from moisture and direct light
- • Keep in original container with desiccant
- • Shelf life typically 12–24 months
Compounded Preparations
- • Follow pharmacy-specific storage instructions
- • Typically store at controlled room temperature
- • Check beyond-use date from compounding pharmacy
- • Keep away from children and pets
Cost & availability
| Source | Cost | Notes |
|---|---|---|
| Compounding pharmacies | $30–$90 per month | Most common source; prescription required |
| Research chemical suppliers | $25–$60 per month | Not pharmaceutical grade; quality varies |
| Telehealth clinics | $100–$250 per month | Includes consultation, labs, and prescription |
| Comparison: TRT | $50–$300+ per month | Enclomiphene comparable cost with fertility advantage |
The bottom line
Enclomiphene is a hormonal compound with research interest in testosterone, hypogonadism, serm, male fertility. While preclinical evidence is encouraging, it remains investigational and is not FDA-approved. Any use should be under qualified medical supervision.
Best for
- • Researchers studying hormonal signaling and endocrine function
- • Individuals interested in testosterone under medical guidance
Not for
- • Self-administration without medical supervision
- • Pregnant or breastfeeding individuals
- • Individuals with contraindicated conditions
Related compounds
Frequently asked questions
References
- [1] Wiehle R, Cunningham GR, Pitteloud N, et al.. Testosterone restoration using enclomiphene citrate in men with secondary hypogonadism: a pharmacodynamic and pharmacokinetic study. BJU Int (2014). doi: 10.1111/bju.12363 PMID: 24053463
- [2] Kim ED, McCullough A, Kaminetsky J.. Oral enclomiphene citrate raises testosterone and preserves sperm counts in obese hypogonadal men, unlike topical testosterone: restoration instead of replacement. BJU Int (2016). doi: 10.1111/bju.13014 PMID: 25345684
- [3] Kaminetsky J, Werner M, Engelman J, et al.. Enclomiphene citrate and testosterone gel for secondary hypogonadism: efficacy, safety, and effects on sperm counts. Fertil Steril (2013).
- [4] Rodriguez KM, Pastuszak AW, Lipshultz LI.. Enclomiphene citrate for the treatment of secondary male hypogonadism. Expert Opin Pharmacother (2016). doi: 10.1080/14656566.2016.1190832 PMID: 27187030
- [5] 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). doi: 10.1016/j.fertnstert.2014.06.004 PMID: 25044085