A new male birth control pill passed tests of safety and tolerability when healthy men used it daily for a month, and it produced hormone responses consistent with effective contraception, according to researchers at two institutions testing the drug.

The Phase 1 study results were presented on March 24 at the Endocrine Society’s annual meeting in New Orleans. Stephanie Page, a professor of medicine at the University of Washington School of Medicine, jointly led the study with Christina Wang, a professor of medicine at UCLA in Los Angeles.

Study results indicate that the experimental male oral contraceptive decreased sperm production while preserving libido. The pill is called 11-beta-methyl-19-nortestosterone dodecylcarbonate, or 11-beta-MNTDC. It is a modified testosterone that has the combined actions of a male hormone (androgen) and a progesterone.

The study involved 40 healthy men across two sites: UW Medical Centre in Seattle and the Los Angeles Biomedical Research Institute in Torrance, Calif. Ten study participants randomly received a placebo capsule, and 30 others received 11-beta-MNTDC at one of two doses; 14 men received 200 mg and 16 got the 400 mg dose.

Subjects took the drug or placebo once daily for 28 days.

Levels of two hormones required for sperm production dropped greatly in the study cohort, compared with those taking the placebo, the researchers reported.

Among men receiving 11-beta-MNTDC, only a few mild side effects were reported, including fatigue, acne and headache in four to six men in each dosage level. Five men reported mildly decreased sex drive, and two men described mild erectile dysfunction, but sexual activity was not decreased, Wang said.

No participant stopped taking the drug because of side effects, and all passed safety tests.

The effects of low testosterone were minimal, said Page, because “11-beta-MNTDC mimics testosterone through the rest of the body but is not concentrated enough in the testes to support sperm production.”

The drug effects were reversible after stopping treatment.

Because the drug would take at least 60 to 90 days to affect sperm production, 28 days of treatment is too short an interval to observe optimal sperm suppression, Wang said. They plan longer studies, and if the drug is effective, it will move to larger studies and then testing in sexually active couples.

11-Beta-MNTDC is a “sister compound” to dimethandrolone undecanoate, the first potential male birth control pill to be tested by the same researchers. Their results were published February 1 in The Journal of Clinical Endocrinology and Metabolism.

“The goal is to find the compound that has the fewest side effects and is the most effective,” Page said. “We are developing two oral drugs in parallel in an attempt to move the [contraceptive medicine] field forward.”

The Eunice Kennedy Shriver National Institute of Child Health and Human Development, which is developing 11-beta-MNTDC and other male contraceptives, funded this study.

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