A preliminary study has shown that a new birth control gel for men dramatically reduced sperm counts with few side effects.
A team headed by Dr. Christine Wang of the Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center enrolled 99 men in the study. The participants were randomly assigned to use one of three unidentified gels on their skin every day for six months. One gel contained testosterone plus placebo, one contained testosterone and 8 mg of progestin, and the third contained testosterone and 12 mg of progestin.
The results indicated that complete absence of sperm occurred in significantly more men who applied the combined testosterone and progestin than testosterone alone: 78 and 69 percent (8 and 12 mg of progestin, respectively). Among the men who used the gel containing testosterone only, 23 percent had complete absence of sperm.
According to Dr. Wang, a sperm concentration less than 1 million sperm per milliliter is compatible with very low pregnancy rates. Sperm counts reached that level in 88 to 89 percent of men who used the testosterone-progestin combinations, depending on the progestin dose. Only 23 percent of the men using the testosterone-only gel had a sperm count lower than 1 million per milliliter. The gel works because 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. According to Dr. Wang it takes about 12 weeks after stopping the gel for sperm counts to return to a normal level. Due to these results, she concludes that this combination of hormones warrants further study as a male contraceptive.