Researchers at Columbia University Medical Center believe they're close to developing a male contraceptive pill with none of the side effects of previous, steroid-based versions.
They've found that low doses of a compound that interferes with retinoic acid receptors (RARs) cause sterility in male mice. And, crucially, normal fertility was restored soon after the drug was stopped.
The discovery came about by accident. Another team had been testing a compound for the treatment of skin and inflammatory diseases - but had abandoned it when they found it was "a testicular toxin".
But when Columbia's professor Dr Debra Wolgemuth came across the paper, she realized the compound was worth testing as a contraceptive.
"We were intrigued," she says. "One company's toxin may be another person's contraceptive."
To investigate whether the compound prevented conception at even lower levels than those cited in the company's study, Dr. Wolgemuth and her team placed the treated male mice with females and found that reversible male sterility occurred with doses as low as 1.0mg/kg of body weight for a four-week dosing period.
The big advantage of the compound, the researchers say, is that it avoids the side effects commonly associated with steroidal hormone-based methods.
These include a variability in efficacy between different races, as well as an increased risk of cardiovascular disease and benign prostatic hyperplasia. Steroids have also been associated with a diminished libido - not terribly helpful.
"We have seen no side effects, so far, and our mice have been mating quite happily," said Dr. Wolgemuth.
Although dietary vitamin A is responsible for the production of light-sensitive receptors in the eye, the researchers say the drug will not affect vision. Unlike steroid-based versions, the compound can be taken orally as a pill.
It'll be a while before the product hits the market, as the researchers need to show that it's safe, effective and reversible when used for years. The team's now planning longer-term studies.