UW School of Medicine researchers are testing a shoulder-rub gel for men that can be more than 90-percent effective in preventing pregnancy.

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It takes two people to make a baby. But to prevent pregnancy, the burden has almost always fallen on the woman.

A new method being tested at the University of Washington aims to change that.

The UW School of Medicine is one of three sites testing a contraceptive gel for men, which works by reducing sperm production when applied daily on the upper arms or shoulders, according to researchers. If the trials are successful, the substance may soon be available to people seeking to avoid unplanned pregnancies whose options traditionally have relied on more than a dozen options for women, including pills, implants, shots, patches and rings, compared with just condoms for men.

“We are neglecting 50 percent of the population with our current methods,” Dr. Stephanie Page, a UW School of Medicine endocrinologist and the study’s principal investigator, said in a phone interview. “There’s every reason for men to be more engaged.”

UW researchers are enrolling about 50 couples for the three-year trial, which started Nov. 28. The testing, which is also being conducted in Los Angeles and Kansas City, Kansas, is funded by the National Institutes of Health. The gel was developed by NIH and the Population Council, an international nonprofit focused on reproductive health.

Participants will receive a clear gel that contains progestin, a hormone used in female birth control, and testosterone to counter the effects of progestin. Men enrolled in the study will apply the gel to each shoulder once a day and, within eight to 16 weeks, their sperm counts should be low enough to prevent pregnancy. Once the count drops sufficiently, couples will receive the go-ahead to use the gel as their only method of birth control for a year.

Page is among a group of UW researchers who have been working on male contraception for decades. But it’s been a challenging area in a field focused primarily on females, according to Dr. William Bremner, a UW professor of medicine who is directing the trial. There’s long been a social bias against birth control for males, he said.

“Among other things, there’s been a perception that pregnancy is ‘the woman’s problem,’ in some people’s view,” he said.

There’s also the “numbers game,” Page said. Women ovulate once a month, and interrupting an ovulation cycle is much easier than trying to decrease production of millions of sperm.

Developing new contraceptive methods is also generally time-consuming because researchers must find ways to minimize negative impacts, such as decreased sex drive, she said.

Other birth-control methods for men that are in early trials at UW include a pill that reduces levels of testosterone and other hormones responsible for sperm production. A monthlong trial of the pill found that the hormones dropped, with few side effects. The method is still being tested on men, with a goal to eventually add it to the scarce pool of options available for them, Page said.

With the gel now being tested, sperm concentration returns to normal numbers within three to four months after the man stops daily use, she said. Researchers will monitor sperm counts throughout the study, but the trial leaders cautioned that pregnancy is still possible. Page said they anticipate the gel will be more than 90 percent effective in preventing pregnancy, making it a more reliable method than condoms, which have about a 13 percent failure rate.

In an earlier trial that involved only men to measure sperm-production levels, some men gained weight while using the gel, but mostly in muscle, Bremner said. Researchers observed that others who had heavy bouts of acne during puberty had recurrences. The researchers will make the potential side effects, including those they don’t know about yet, very clear to the couples, he added.

Bremner and Page estimate the gel could be available to consumers in five to 10 years, depending on the results of the current trial and others that will follow.

Regardless of how effective the substance proves, the opinion they said they often hear is that people wish more options were available sooner.

“Attitudes have changed in both men and women in what they find acceptable,” Bremner said. “We think the time is right. People are ready for it.”