People in homosexual relationships are routinely excluded from clinical trials, especially those related to sexual health, according to a new study.

An analysis of US clinical trials by researchers from the Fox Chase Cancer Center in Philadelphia searched for trials involving the terms “couples”, “erectile dysfunction” or “hypoactive”. Of the 243 studies they found, 37 explicitly excluded lesbians and gay men, they report in the New England Journal of Medicine.

“Most gay and lesbian patients are probably unaware that their sexual orientation is being used as a screening factor for clinical trial participation,” says study author Brian Egleston. “This is a potentially significant issue, both for patients and the medical research community.”

Industry sponsored and multi-region trials were especially likely to exclude lesbians and gays. Although there may be legitimate reasons to exclude potential trial participants based on sexual orientation, the authors say researchers should be “held to careful scientific reasoning” if they wish to do this. In addition, requiring patients to be in heterosexual relationships may also exclude unmarried or unpartnered hetro- and homo-sexual people.

“It’s not unusual in studies to decide who your target population is and exclude people who are not in this target population,” Susan Cochran, of the University of California, Los Angeles School of Public Health, told ABC. “The bigger problem is if everyone just decides they’re going to exclude sexual minorities. Then their health issues are never dealt with.”