The injection consisted of synthetic testosterone and progestin and was administered every six to eight weeks to 320 men between the ages of 18 to 45. According to Dr. Seth Cohen, the combination is enough to trick the brain into thinking that the body is producing enough testosterone, so the body stops producing its own testosterone and sperm.
Overall, the study found that the injection was 95 percent effective, which is slightly less than the 99.9 percent effectiveness associated with perfect use of the female birth control pill. However, 20 men dropped out of the study early, citing adverse side effects including depression, mood disorders, injection site pain, muscle pain, increased libido and acne.
“I immediately thought of the recent findings on female birth control,” Indiana University Bloomington biology professor Elisabeth Lloyd told CNN. The study she referred to found that there is a strong association between hormonal contraception for women and depression.
“Twenty or 30 percent of the women who take oral birth control pills experience depression and have to take medication for it. So the difference just struck me,” Lloyd added. “They terminated this study once it showed 3 percent depression for men.”
Side effects aside, researchers say most men recovered and returned to normal fertility after the last injection.
“The minimum recovery time was about 12 weeks after the last injection and the average time was about 26 weeks,” said the study’s co-author Doug Colvard. However, eight men did not return to normal fertility after a year, and one did not fully recover after four years.
“It shows that it’s a risk, a low-probability risk of it, and it’s not to be sneezed at as a risk of it, surely,” Lloyd said. She added that the risk of side effects and infertility for this injection should be weighed against the side effects and fertility risks women experience with contraception, including strokes and blood clots.
“These risks of fertility damage are not fatal risks like the women endure with their birth control,” Lloyd said. “You have to compare what women are doing in terms of taking hormones with what men are doing in terms of taking hormones.”