Male contraceptive drug is 100% effective in mice

A male contraceptive that immobilizes sperm for 2 hours prevented pregnancy in mice and caused no adverse side effects

By Grace Wade

A drug that temporarily paralyzes sperm could become the first on-demand male birth control pill. In mice, the contraceptive was 100% effective in preventing pregnancy for about 2 hours, with full fertility returning 24 hours later.

“It is, in the field of male contraception, totally revolutionary”, declares Jochen Buck at Cornell University in New York. Most other potential male contraceptives in clinical development are only effective after eight to 12 weeks, he says.

Previous research has shown that sperm need a protein called soluble adenylyl cyclase (sAC) to move around, and men who cannot produce sAC due to rare genetic mutations are infertile. So Buck and colleagues assessed whether a drug-inhibiting sAC could be used as a male contraceptive. If sperm are immobile, they cannot move up the vaginal tract to fertilize an egg.

The team assessed the movement of sperm taken from 17 male mice, eight of which received the drug. In samples taken 2 hours after mice received the drug, only about 6% of sperm were motile on average, compared to about 30% in control mouse samples. The effect wore off after about 24 hours, “which means we not only have an on-demand contraceptive, but also a rapidly reversible contraceptive,” explains Melanie Balbachalso at Cornell University.

In another test, researchers paired 52 male mice with females 30 minutes after giving the males the contraceptive drug. After 2 hours, each couple had mated, but there were no pregnancies, indicating that the contraceptive was 100% effective. The drug also did not cause any noticeable side effects, even when the mice were given three times the standard dose of a comparable compound continuously for 42 days.

“What I like about the contraceptive offered in this study is the on-demand option,” says Ulrike Schimpf at the KTH Royal Institute of Technology in Sweden. “It would act quickly, temporarily and is effective from the first dose.”

Buck and Balbach plan to refine the drug so it lasts longer before testing it in humans. If all goes well, they hope to start clinical trials by 2025.

“We need more [birth control] options, and men need an option so that the burden of contraception is no longer on women,” says Balbach. “We are very optimistic that once men take the inhibitor it will have the same effect.”

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