Male contraception injection is 96% effective, but side effects meant the trial had to stop

A trial of a male contraception injection has been found to be 96% effective. However, researchers had to stop it because of unwanted side effects including mood swings, depression, acne and increased libido.

The search for a hormonal birth control method for men is ongoing. While women have a number of options available to them, men are largely limited to condoms.

In a study published in the Endocrine Society's Journal of Clinical Endocrinology & Metabolism, an international team of researchers has released the results of a trial that took place between 2008 and 2012. In it, 320 heterosexual healthy men aged between 18 and 45 in monogamous long-term relationships were given hormonal injections that supressed their sperm counts.

They were given two injections every eight weeks for up to 26 weeks until their sperm counts had been lowered to the point at which they met the criteria for the next part of the trial. During this period, they were asked to use other methods of birth control.

Once their sperm was sufficiently lowered, however, they were asked to rely on the injections alone. They continued to get injections every eight weeks and they continued to do so for up to 56 weeks. They provided semen samples every eight weeks to make sure their sperm count remained below the required level. On stopping the trial, researchers monitored them to ensure their sperm count returned to normal.

During the period where couples relied on the injections, there were four unplanned pregnancies. The male contraceptive was found to be almost 96% effective against pregnancy across the whole trial.

However, the trial had to be stopped because of the side effects reported. Men reported depression and mood disorders, muscle pain, pain at the site of injection, increased libido and acne. Twenty men dropped out of the trial because of the side effects. Despite the side effects, 75% of participants said they would use it as a method of contraception after completing the trial.

Concluding, scientists said this was the first large-scale, multi-country trial of its kind and should provide an "important reference" for safety trials of male contraception. "More research is needed to advance this concept to the point that it can be made widely available to men as a method of contraception," said study author Mario Festin said. "Although the injections were effective in reducing the rate of pregnancy, the combination of hormones needs to be studied more to consider a good balance between efficacy and safety.

"The study found it is possible to have a hormonal contraceptive for men that reduces the risk of unplanned pregnancies in the partners of men who use it. Our findings confirmed the efficacy of this contraceptive method previously seen in small studies."