Routine hormone injections into the buttocks of 320 men caused a dramatic drop in sperm count and prevented pregnancies during an early one-year phase, researchers reported Thursday.
The findings suggest that a future hormonal contraceptive for men could one day be possible. However, the data also revealed many side effects, such as acne and mood swings, suggesting that much work is still needed before such a contraceptive method becomes a reality.
“A male hormonal contraceptive is possible,” lead author Mario Festin, a physician in the World Health Organization’s division of reproductive health and research, told the Chicago grandstand. “We must continue to search for or research the right drugs, and their combinations, with the highest efficacy and safety, and acceptability, with the fewest side effects.”
Previous work showed that high doses of testosterone could wipe out sperm counts in men, but they also caused side effects. Lowering the dosage level with a steroid hormone known as a progestin that activates the progesterone receptor was a possible solution.
In the new study, published in the Journal of Clinical Endocrinology and Metabolism, gave Dr. Festin and colleagues gave men ages 18 to 45 injections into their buttocks once every eight weeks during a 24-week “suppression phase.” The injections contain 200 mg progestogen and 1000 mg testosterone. By the end, nearly 96 percent of those who stayed in the study (some dropped out) saw their sperm count drop to less than 1 million per milliliter. (Normal levels can range from 15 to over 200 million/ml.)
From there, 266 men with sperm suppression went into a “testing” phase for up to 56 weeks. All of the men were in monogamous, heterosexual relationships and at this point in the process they were asked to give up alternative forms of birth control. (Their female partners were also screened at the beginning of the entire trial. They had to have no desire to have a child within a two-year period, but also be willing to accept a low risk of pregnancy.) The men were given injections all the time every eight weeks and their sperm counts were checked.
During the testing phase, four women became pregnant and six men saw their sperm count bounce back. If we count the failure rate during the “suppression phase”, the overall failure rate of the hormone shots was 7.5 percent, that is, the shots had a success rate of 92.5 percent.
However, many of the men reported side effects. Nearly half of the 320 men (46 percent) reported developing acne. Thirty-eight percent reported an increased sex drive. Twenty-three percent had injection site pain and 17 percent had emotional disturbances.
After the study was completed, five percent of the men did not recover their sperm count in the year after their last injection.
Still, in the end, more than 75 percent of participants said they would be willing to use the birth control method in the future if it were available. The study’s authors concluded that the method was “relatively good” but needed adjustments.
The National Health Service in England noted that condoms are still clearly the better bet, with an effective rate of 98 percent when used correctly.
Journal of Clinical Endocrinology and Metabolism2016. DOI: 10.1210/jc.2016-2141 (About DOIs).