It’s been a big week for male birth control: Hot on the heels of the discovery of a male contraceptive that can be snorted, a new study introduces a hormone cocktail that can be injected instead.

The birth control shot, introduced in a study in the Journal of Clinical Endocrinology & Metabolism, published Thursday, dramatically reduces the amount of sperm swimming in a man’s semen, dramatically cutting down his chances of fathering an oopsie-baby to near zero. With an excellent effectiveness rate of 96 percent, the contraceptive is more trustworthy than the other fertility options for men, which include condoms and the laughably impotent withdrawal method. It has the potential to allow couples to stop relying on female contraceptives, which can make it difficult for partners trying to conceive.

A new injectable male birth control is very effective at preventing pregnancies, but could lead to depression.
A new injectable male birth control is very effective at preventing pregnancies, but could lead to depression.

If it sounds too good to be true, that’s because there’s a big catch: One side effect of these contraceptives is depression. In the study of 320 healthy, adult men, who received regular injections of the contraceptive, 20 participants eventually dropped out, and reported problems that included mood disorders, like depression, as well as injection site pain, muscle pain, increased libido, and acne.

Over the course of the study, carried out by Swiss researchers, participants reported a total of 1,491 “adverse events,” which included serious cases, such as one man with depression, another who intentionally overdosed on acetaminophen, and one who developed an abnormally rapid and irregular heartbeat after he stopped receiving the drug. There was even one suicide that took place during the trials, although it was determined not to have been caused by the drug.

Eventually, the side effects were deemed so serious that the study authors stopped enrolling people in the trial in 2011.

But despite the troubling side effects, more than 75 percent of the men in the study said they’d be willing to use this form of birth control by the end of the trials. The side effects, after all, are to be expected in any hormone-based drug — the female Pill, for instance, has long been known to trigger mood changes and physical pain — but the researchers are continuing to refine it in order to spare men the discomfort.

Photos via Getty Images / Joe Raedle

Yasmin is a writer and former biologist living in New York. A Toronto girl at heart, her writing also appears in The Last Magazine and SciArt in America. You might recognize her as a past host of Scientific American's YouTube series.