Men might one day be able to slather a gel on their backs and shoulders that protects against getting their partners pregnant.
In a recent six-month trial involving 68 men, 89 percent of those who were treated with a gel containing the male hormone testosterone and the female hormone progestin experienced sperm counts so low that pregnancy would be highly unlikely, researchers said. The men reported no effects on their sex drive.
"This approach using hormones to suppress sperm production can work in a majority of men," said study researcher Dr. John Amory, a professor of medicine at the University of Washington in Seattle. However, the gel is far from being ready for use in the general population, he said. It would have to work for at least 98 percent of men before it would be a viable male birth control option.
Researchers could possibly increase the gel's effectiveness by adding another component to it that suppresses sperm production. Or, it could help to figure out how to select which men will experience effective sperm suppression when using the gel, Amory said.
In any case, the findings will need to be replicated in larger groups of patients, and long-term data on the gel's safety and effectiveness are needed.
The findings were presented at a research conference in June. The work has not been published in a peer-reviewed scientific journal.
In the study, which was conducted jointly by researchers at Washington and Harbor-UCLA Medical Center in Torrance, Calif., 99 men were randomly divided into three groups. One group was given a gel containing testosterone, and the other groups were given gels containing both testosterone and progestin, but contained different progestin concentrations.
The researchers used the benchmark of a sperm count of 1 million sperm per milliliter because that level means the chance of pregnancy is less than 1 percent per year, Amory said.
Results showed that 88 percent of men who used one of gels with testosterone and progestin, and 89 percent of men who used the other gel with both hormones (which had a slightly lower progestin concentration) experienced sufficiently lowered sperm counts. Among the men using the gel that contained only testosterone, 23 percent experienced sperm counts lower than the 1 million mark.
The gel has to be applied daily to be effective, Amory said. It takes two or three minutes to apply, but men need to wait about five minutes before getting dressed, to give it time to soak in.
About a third of the 99 men originally enrolled in the study stopped using the gel before reaching the 20-week mark, so they were not included in the researchers' analysis of the gel's effectiveness, Amory said.
All the men's sperm counts returned to normal after they stopped using the gel, the researchers said.
The most common side effect that the men reported was acne — 25 percent said they had the skin problem after using the gel. For some, this may have contributed to their stopping use of the gel, Amory said. Some of the men also noticed a bit of weight gain, he added.
How it works
Because testosterone is broken down easily by the liver if it's ingested orally, male birth control options are currently seen as limited to either injections or skin lotions.
"The good news from this study is, you can get away from injections," Amory said.
However, a transdermal approach has its drawbacks, he said. There are concerns that women and children who have physical contact with a man using the gel could be exposed to potentially damaging levels of hormones.
The hormones in the gel have their effect not directly on the testes (where sperm are produced), but instead on the pituitary gland, which is found near the brain, Amory explained. The hormones signal the pituitary gland to stop producing two hormones — called follicle-stimulating hormone and luteinizing hormone — which normally signal the testes to produce sperm cells and testosterone. The net effect is that testes stop producing sperm cells, but the man's testosterone levels don't take a hit, because he receives the hormone in the gel.
Pass it on: A gel containing the hormones testosterone and progestin could one day be an option for reversible birth control for men.