WASHINGTON - Researchers are developing a hormonal contraceptive for men that is completely reversible and has shown promise in an early test.
The contraceptive is made up of two gels. One contains a progestin - a synthetic version of the female hormone progesterone - and the other, the male reproductive hormone, testosterone. The combination suppresses the production of sperm by lowering levels of male hormones.
In a preliminary study, applying the hormonal contraceptive to the skin each day reduced sperm counts to below the levels normally needed for reproduction.
Leading the research was Christina Wang, a professor of medicine with the Los Angeles Biomedical Research Institute at the University of California Medical Center.
Wang says the gels had few adverse side effects, the major one being an increase in acne in some of the men.
"And we don't know, but we think that maybe the testosterone dose that was given was slightly higher than what the men's own testosterone (level) was," Wang said.
In larger clinical trials, Wang says men will be given a smaller dose of testosterone.
Fifty-six healthy men completed the six-month preliminary trial of the contraceptive gels. About 90 percent of those who received the combination of hormones had a sperm concentration of less than one million sperm cells per milliliter, essentially rendering them infertile. Among the men using the testosterone-only gel, only 23 percent experienced those same low sperm counts.
Regine Sitruk-Ware is a reproductive endocrinologist with the Population Council in New York, a non-profit group whose researchers developed Nestorone, the synthetic progestin used in the gel. In higher doses than those naturally produced in women, the progestin molecule acts on the pituitary gland in the brain to block the production of sperm. But used alone, Sitruk-Ware says Nestorone causes side effects, including a reduction in libido. That's why testosterone was included in the contraceptive mix.
Sitruk-Ware says it takes at least 30 days for the gel to block production of sperm, so the hormonal contraceptive is not something that works immediately like a pill. And about a month after a man stops applying it, the contraceptive effects wear off.
Sitruk-Ware says studies on four continents show a majority of men would support a hormonal form of birth control in addition to condoms and vasectomy, a surgical procedure for male sterilization.
"It's something that they can use themselves. It doesn't need a health provider to insert an implant or to make an injection. So the concept of a gel was seen very positively," Siturk-Ware said.
Before larger trials begin, the hormones will be reformulated into a single gel, making the contraceptive easier to apply. Researchers say the regulatory approval process means it will be several years before a male contraceptive gel comes to market.
Results of the preliminary study of a combination Nestorone and testosterone male contraceptive were presented at a recent meeting of the Endocrine Society in Houston, Texas.