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Male contraceptive pill proves safe in first stage clinical trial
Last reviewed: 27.07.2025
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YourChoice Therapeutics, in partnership with Quotient Sciences and Incyte, reports that single oral doses of the investigational non-hormonal male contraceptive YCT-529 up to 180 mg did not result in clinically significant safety concerns in 16 healthy men.
Unintended pregnancies account for about half of all conceptions worldwide, with men relying almost exclusively on condoms (13% failure rate) or vasectomy to prevent pregnancy. Earlier attempts at non-hormonal drugs, such as WIN 18,446 and gossypol, reduced sperm production but caused reactions when alcohol was consumed or hypokalemia, leading to research being abandoned for decades.
About the study
In a study titled “Safety and pharmacokinetics of the non-hormonal male contraceptive YCT-529,” published in Communications Medicine, researchers conducted a randomized, double-blind, placebo-controlled, dose-escalation study to evaluate the safety, tolerability, pharmacokinetics, and preliminary pharmacodynamic effects.
Sixteen vasectomised men aged 32–59 years (BMI 21.9–31.1 kg/m²) were given either YCT-529 capsules (n=12) or placebo (n=4) at Quotient Sciences in the UK. The capsules were taken with water. Continuous ECG monitoring, serial blood draws, sexual activity and mood diaries and inflammatory biomarkers were performed for 336 hours post-dose.
Results
There were no serious or severe adverse events. One participant experienced a transient asymptomatic arrhythmia at the 90 mg and 180 mg doses; cardiac evaluation revealed no structural abnormalities. ECG modeling showed that the upper bound of the 90% confidence interval of the QTc interval remained below the 10 ms threshold of regulatory concern at all dose levels.
Blood, coagulation, urine tests and general clinical profile revealed no abnormalities of clinical significance.
The median time to peak plasma concentration (Tmax) ranged from 4 to 10 hours, and the geometric mean half-life ranged from 51 to 76 hours. Food increased peak concentration and total drug exposure, but high variability after meals made interpretation of the data difficult.
Efficacy and hormonal profile
At a dose of 180 mg, exposure (AUC0–24 ≈ 27,300 h ng/mL) reached levels previously associated with reversible infertility in non-human primates.
Levels of testosterone, luteinizing hormone, follicle-stimulating hormone, and sex hormone-binding globulin remained within reference ranges.
Self-reported libido, mood, and sexual function were unchanged. Inflammatory markers remained stable, with the exception of a transient diet-related increase in IL-6.
Conclusions
Single doses of YCT-529 achieved blood concentrations that suppressed spermatogenesis in preclinical studies, without effects on hormonal balance, mood, or cardiac conduction.
The drug has successfully passed a key safety assessment phase required for the development of male contraceptives.
A repeated-dose study is currently underway to evaluate its effects when taken for 28 and 90 days.