Some clinical research trials are explicitly excluding gays and lesbians, a study has found.

Research sponsored by the US National Institutes of Health, the US government and private companies found that 15 per cent of the trials were found to bar gay people.

Clinical trials on sexual dysfunction were the most likely to exclude gays and lesbians, the survey of 237 clinical trials found.

Single men and women were also more likely to be barred, while gays were most likely to be excluded from trials which were sponsored by industry, held across several states or were at a late stage of testing.

Study author Brian Egleston of the Fox Chase Cancer Center, told AFP: “Most gay and lesbian patients are probably unaware that their sexual orientation is being used as a screening factor for clinical trial participation.

“Researchers should be held to careful scientific reasoning when they develop exclusion criteria that are based on sexual orientation.”

He added: “This is a potentially significant issue, both for patients and the medical research community.”

Mr Egleston wrote a letter to today’s New England Journal of Medicine to raise the issue.

Although some surveys, such as those on heterosexual HIV transmission, may have reasonable cause to exclude gays, Mr Egleston found that in some cases, there was no clear reason for barring them.