The daily transdermal use of a combination gel containing Nestorone and testosterone suppressed sperm production faster than expected, according to research presented at ENDO 2024, the Endocrine Society's annual meeting in Boston, Mass.

The study evaluated the time to sperm suppression in healthy males using a daily application of a combination gel containing 8 mg of Nestorone (segesterone acetate) and 74 mg of testosterone. This phase 2b clinical trial aimed to assess the contraceptive efficacy, safety, acceptability, reversibility, and timeline to sperm suppression.

"A more rapid time to suppression may increase the attractiveness and acceptability of this drug to potential users," said senior researcher Diana Blithe, Ph.D., chief of the Contraceptive Development Program at the National Institutes of Health (NIH) in Bethesda, Md.

The study included 222 men who completed at least three weeks of daily treatment with the contraceptive gel. Early in the study, researchers measured sperm production suppression by obtaining sperm count tests at four-week intervals. The threshold for effective contraception was defined as 1 million or fewer sperm per milliliter of semen.

Results showed that 86% of participants achieved sperm suppression within 15 weeks. Among these men, the median time to suppression was less than eight weeks. Prior studies of male hormonal contraceptives given by injections showed a median suppression time between 9 and 15 weeks.

The researchers noted that testosterone treatment alone decreases sperm production, with a median time of 15 weeks. The addition of segesterone acetate in the gel formulation not only sped up the time to suppression but also reduced the required dose of testosterone, maintaining normal sexual function and other androgen-dependent activities.

"The development of a safe, highly effective, and reliably reversible male contraceptive method is an unmet worldwide need," study investigators noted. "While studies have shown that some hormonal agents may be effective for male contraception, the slow onset of spermatogenic suppression is a limitation."

The sperm suppression stage of this international phase 2b trial is complete, and the study continues to evaluate the contraceptive's overall effectiveness, safety, acceptability, and the reversibility of contraception after treatment stops.

No conflicts of interest were disclosed.