For some time, scientists have been working to develop an effective birth control pill for men. Now, study findings presented at ENDO 2018, the endocrine society’s annual meeting, suggest that the experimental oral contraceptive for men dimethandrolone undecanoate (DMUA) is showing early signs of potential, reports the Endocrine Society.

Researchers tested three different doses of DMAU (100, 200 and 400 milligrams) and two different formulations inside the capsules (castor oil and powder) on 100 healthy men, ages 18 to 50. Scientists randomly assigned participants in each dose group either an inactive placebo or DMAU taken once daily with food for 28 days. (In order for DMAU to be effective, it must be taken with food.)

Eighty-three men completed the study. Participants provided blood samples for hormone and cholesterol testing on the first and last days of the study.

Findings showed that individuals who took 400 mg of DMUA exhibited marked suppression of testosterone and two hormones required for sperm production. (Low levels were also consistent with effective male contraception shown in longer-term studies.)

In addition, not many men reported symptoms associated with either insufficient or excessive amounts of testosterone. All participants that took DMUA, however, experienced mild weight gain and slight reductions in HDL (the “good” cholesterol). But everyone passed safety tests that included markers for liver and kidney function.

“These promising results are unprecedented in the development of a prototype male pill,” said Stephanie Page, MD, PhD, a professor of medicine at the University of Washington in Seattle and the study’s senior investigator. “Longer-term studies are currently under way to confirm that DMAU taken every day blocks sperm production.”

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