The world is said to be closer than ever to a male birth control pill, but researchers say problematic side effects may stop it from going ahead.
Study results from trials of the developing pill were presented at the Endocrine Society's annual meeting in Los Angeles over the weekend.
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The doctors behind the study say the first trial involved 40 healthy men, aged 18 to 50, including 10 who received a placebo.
Despite low testosterone levels in the men taking the drug, researchers reported "no serious adverse events". However, trial participants had issues with cases of fatigue, headache, acne, decreased libido and mild erectile dysfunction.
Five men (17 percent) reported a "mildly decreased" sex drive. Two (seven percent) experienced mild erectile dysfunction, although reportedly "sexual activity was not decreased."
It's worth noting that side effects have affected many women since the US Food and Drug Administration first approved the female contraceptive in 1960. Common side effects women who take the pill deal with include fatigue, headaches, blood clots, acne and low sex drive.
The male birth control pill study's co-senior investigator, Dr Christina Wang, says the early results look promising.
"Our results suggest that this pill, which combines two hormonal activities in one, will decrease sperm production while preserving libido," she said during the presentation, reports Technology Networks.
"Safe, reversible hormonal male contraception should be available in about 10 years.".
Researchers are also looking at different means of a contraceptive, including an injection and a topical gel.
Trials in the UK in 2016 showed a contraceptive injection for men was almost as effective as the female pill, as it was 96 percent effective in preventing pregnancy. Side effects of the male contraceptive injection are also still being tested.