Other contraceptive methods include vaginal rings and the morning-after pill. Photo: IC

A team of scientists said Wednesday they had developed a male oral contraceptive that was 99 percent effective in mice and didn't cause observable side effects, with the drug expected to enter human trials by the end of 2022.

The findings will be presented at the American Chemical Society's spring meeting, and mark a key step toward expanding options for men.

Ever since the female birth control pill was first approved in the 1960s, researchers have been interested in a male equivalent, Md Abdullah Al Noman, a graduate student at the University of Minnesota who will present the work, told AFP.

"Multiple studies showed that men are interested in sharing the responsibility of birth control with their partners," he said - but until now, there have been only two effective options: condoms or vasectomies. 

The female pill uses hormones to disrupt the menstrual cycle, and historic efforts to develop a male equivalent targeted the male sex hormone testosterone. The problem with this approach, however, was that it caused side effects such as weight gain, depression and increased levels of a cholesterol.

To develop a non-hormonal drug, Noman, who works in the lab of Professor Gunda Georg, targeted a protein called "retinoic acid receptor [RAR] alpha."

Inside the body, vitamin A is converted into different forms, including retinoic acid, which plays important roles in cell growth, sperm formation, and embryo development.

Retinoic acid needs to interact with RAR-alpha to perform these functions. 

For their work, Noman and Georg developed a compound that blocks the action of RAR-alpha. 

AFP