For many couples, the numerous options for birth control still come with plenty of hassles. But scientists are working on an alternative approach that might be more appealing for some: a non-hormonal male birth control pill with possibly very few side effects.

The drug is codenamed YCT-529, and it’s being developed by the company YourChoice Therapeutics, in conjunction with researchers from the University of Minnesota and others. In early human trial results published this week, YCT-529 appeared to be safe and tolerable. The drug is now being tested in larger-scale studies.

YCT-529 (previously known as GPHR-529) targets how the body interacts with vitamin A, which helps maintain fertility in mammals. It blocks a protein that binds to a form of vitamin A (retinoic acid) in our cells, known as retinoic acid receptor alpha (RAR-α). By selectively blocking RAR-α and not other similar proteins, the hope is that YCT-529 will reduce sperm production to zero without causing any major side effects. Importantly, this process is also meant to be reversible once people stop taking the drug.

The company began its first clinical trial of YCT-529 in late 2023, and the findings of the trial were published this week in Communications Medicine. It involved 16 healthy men who received either a daily placebo or varying doses of YCT-529; some were also given the drug in combination with food.

Phase I trials are primarily intended to test a drug’s safety, and YCT-529 seemed to pass with flying colors. Compared to controls, the men on YCT-529 experienced no changes in their heart rate, sex drive, mood, or levels of fertility-related hormones. In fact, no adverse events likely related to the drug were documented at all, the researchers found. There was some evidence that food might slow people’s absorption of the drug, though more study is needed to know for sure.

“These results warrant further clinical development of YCT-529,” the study authors wrote.

As promising as this data looks, it is still very early days. That said, YourChoice Therapeutics has already forged ahead with a larger Phase II study of YCT-529. And the race to create the world’s first reversible male birth control is only heating up. Other research teams and companies have developed contraceptive gels and implants that have also shown promise in human trials so far. Soon enough, men will hopefully have several birth control options to pick from, just like women.