"This is the first time that testosterone and Nestorone have been applied to the skin together to deliver adequate amounts of hormones that suppress sperm production," said lead investigator Christine Wang, MD, professor, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center (LA BioMed), according to Medical Xpress
. "Men can use transdermal gels at home—unlike the usual injections and implants, which must be given in a health care provider's office."
As io9.com notes
, this isn't the first time that testosterone and progestin have been used together in hopes of creating a male contraceptive.
In men, progestin enhances the contraceptive effectiveness of testosterone. Both testosterone and progestin work together to turn off hormones that control the production of sperm, lowering sperm count.
To test the effectiveness of the new gel, researchers recruited 99 healthy male volunteers. The participants were then randomly assigned to three groups and given one of three transdermal gels: either testosterone and placebo or testosterone and either 8 mg or 10 mg of Nestorone, the investigational synthetic nonandrogenic progestin. They were asked to apply the gels daily for 20-24 weeks, and 56 complied.
Among those who completed the study, according to the Los Angeles Times
, Wang reported that 88% to 89% of the men receiving the drug combination achieved a sperm concentration of less than 1 million sperm per milliliter,
(a level that previously has been proven to provide contraception), compared with men on testosterone/placebo gels.
After treatment stopped, sperm concentrations recovered to greater than 3 million/mL in all subjects by 40 weeks after the start of the study.
Also, no serious side effects were seen. In prior studies, progestin produced side effects such as acne and changes in cholesterol levels. But Nestorone has no androgenic (male hormone) activity, limiting those side effects.
The next step, investigators said, is to test the combination in a study that recruits couples, asking participants not to use other contraceptives, the Family Practice News Digital Network reports
. In the current study, men were required to use a proven method of contraception and not rely on the gels.
All in all, says the Times, the drug combination "warrants further study as a male contraceptive," but for now it has the potential to become the first effective chemical birth control agent for men.