A birth control gel for men sharply lowered sperm counts with few side effects, researchers reported Tuesday. The gel, containing testosterone and a synthetic progestin called Nestorone, will require substantially more testing, but it has the potential to become the first effective chemical birth control agent for males.
The male hormone testosterone can turn off the production of reproductive hormones controlling the production of sperm. Progestin, a synthetic hormone similar to the naturally occurring hormone progesterone, can amplify the effects of testosterone. The two have been used together in the past in pills, implants or shots, but progestin has androgenic effects that can produce side effects such as acne and changes in cholesterol levels. Nestorone is a new synthetic progestin, developed by the Population Council, that apparently does not have those side effects.