Male birth control pill may soon be a reality

US researchers have stumbled on a compound that may finally lead to a birth control pill for men.

In lab experiments, male mice given the pill were rendered completely infertile during treatment as they produced fewer and less mobile sperm. The drug, originally tested as part of a broader cancer research project, does not affect the hormone system or sex drive, the team said on Thursday.

"There is no effect on the mouse's mojo. The animals exhibit the normal sexual behaviors ...." said James Bradner of the Dana-Farber Cancer Institute in Boston, whose study appears in the journal Cell.

What's more, the effect is completely reversible. Once doctors stopped giving the drug to mice, they were able to sire healthy litters, with no apparent side effects, Dr. Bradner said.

The study is "an exciting report that could have major scientific and social impacts," said Professor Moira O'Bryan, head of the Male Infertility and Germ Cell Biology Laboratory at Monash University in Australia.

The social impact of effective contraception was huge, separating sexuality from reproduction. The Pill – oral contraception for women first introduced in 1960 – promised women almost unlimited freedom from worry about pregnancy because, for the first time, they could control their fertility. This "sexual revolution" lead to more relaxed attitudes about sex outside of marriage and had a significant effect on women's ability to plan their families and careers. Among American women who use contraceptives today, the largest proportions use the Pill – 28 percent  – according to the Guttmacher Institute.

The Pill significantly tipped the balance of responsibility – including costs – for contraception to women. An effective contraceptive pill for men might expand  their involvement in contracption and reproductive decisions.

Scientists say the research is exciting because it applies a unique approach to the problem of male contraception, which is now largely comprised of less reliable methods like condom use, or more permanent procedures like vasectomies.

Bradner's lab focuses on cancer drug research but developed a compound that appears to target a protein specific to the testes called BRDT which instructs sperm to mature. Bradner said the compound does not appear to do damage to sperm-making cells, but they forget how to create mature sperm while under the influence of the drug.

Bradner reached out to reproductive health expert Martin Matzuk of Baylor College of Medicine, another author of the report, and his team tested the compound in mice.

What they found is that the animals began producing fewer sperm, and the ones they did produce were poor swimmers.

"When the drug is removed, these instructions return," Bradner said.

William Bremner from the University of Washington in Seattle, who was not involved in the research, said in a commentary the finding was "a breakthrough new approach," noting that there has not been a new reversible contraceptive for men since the development of the condom centuries ago.

"It's exciting basic science that provides a new approach to think about how a contraceptive for men might be designed," Bremner said in a telephone interview. "At the same time, it's a long ways from being in clinical trials in men, let alone being on pharmacy shelves."

Other teams have developed hormonal pills that are effective, but they disrupt hormone balance in men, Bremner said.