When it was first approved for use in the 1960s, the female birth control pill revolutionised contraception. For those who could take it, it was convenient, affordable and effective.
But in the decades since, creating a male equivalent that is equally successful has proven incredibly difficult, leaving men who want to play their part in a couple’s birth control strategy limited to condoms, which are single-use and prone to failure, or vasectomies, which require surgery and are largely irreversible.
To complicate matters further, most drugs currently undergoing clinical trials target the male sex hormone testosterone and can potentially lead to unpleasant side effects such as depression, weight gain and increased cholesterol levels.
Now, researchers at the University of Minnesota in Minneapolis may have figured out a solution. They have created an oral, non-hormone-based pill that is 99 per cent effective in preventing pregnancies in mice.
“The facts say that men produce 1,500 sperm per heartbeat, but for women there is usually one ovum per cycle. So, to stop this large amount of sperm production we need a really effective method,” said co-author Md Abdullah al Noman, who presented the study at the spring meeting of the American Chemical Society in San Diego.
“So far, the compound that we are reporting in this meeting shows really promising results without any observable side effect in mice.”
The team’s drug, named YCT529, shuts off a protein called the retinoic acid receptor alpha (RAR-α) that binds to vitamin A and plays an important role in cell growth, including sperm formation.
They gave male mice one dose of YCT529 every day for four weeks. They found that it dramatically reduced the sperm counts of the mice and was 99 per cent effective in reducing pregnancies in the test group.
They also found that the mice were able to sire pups after they stopped taking the drug for four to six weeks.
The team hope that human clinical trials will begin on YCT529 later this year but have already started working on a new version of the drug.
“We are trying to make a newer second-generation compound that would be effective in a lower dose,” said Noman. “Sometimes a lower dose could mean higher toxicity, I have to give that caveat, but in most cases a lower dose is better.
"Now we are trying to make a compound that will hit two targets at the same time - retinoic acid receptor alpha and retinoic acid receptor gamma.
“Retinoic acid receptor gamma is also essential for sperm production, so if we could selectively hit these two targets, we hope that we could get the same effect with a lower dose.”
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