Researchers have found injecting two different hormones into men every two months suppressed their sperm production enough to function as a birth control.
Researchers have found injecting two different hormones into men every two months suppressed their sperm production enough to function as a birth control, according to a new study.
However the study was halted due to safety concerns.
Side effects, which included depression and other mood disorders, outweighed the potential benefits of the injections an independent safety board found.
"Researchers are trying to identify a hormonal male contraceptive that is effective, reversible, safe, acceptable, affordable, and available," the study's technical team wrote in an email.
The researchers, led by Dr. Hermann Behre of Martin Luther University of Halle-Wittenberg in Germany, recruited 320 healthy men ages 18 to 45 from several countries.
Four pregnancies occurred among 266 couples over 56 weeks of follow up, the researchers report in the Journal of Clinical Endocrinology and Metabolism.
The failure rate of this form of birth control was 7.5 percent, they found.
The US Centers for Disease Control and Prevention says male condoms have a failure rate of 12 percent.
In women, birth control pills, patches and rings have a failure rate of about 9 percent.
Failure rates are below 1 percent for female implants and intrauterine devices and sterilisation surgeries in both men and women.
Nearly 1,500 adverse events were reported during the study. More than half of those were directly linked to the injections.
Men reported side effects such as acne, injection site pain, increase in libido and several mood disorders, including emotional disorders, hostility, depression and aggression.
In addition to safety concerns, there are other unknowns about this approach to birth control, said Dr Landon Trost, who is head of andrology and male infertility at the Mayo Clinic in Minnesota.
It's important to realise, he added, that this form of birth control - unlike condoms - would not protect against sexually transmitted infections or disease.
"The question is what is the real practical role for this," Trost said.
The World Health Organisation, whose researchers were among those who worked on the new study, currently recommends condoms and sterilisation as the only forms of male birth control.