A trial study of gay men taking medication to prevent HIV infection suggests that it does not encourage them to have riskier sex.

Viread, produced by Gilead Sciences Inc, is already used for the treatment of HIV infections but is being tested to see if it can be used to prevent HIV infection before exposure to the virus.

The study was designed primarily to test whether Viread produced side effects, rather than analysing its effectiveness or effect on behaviour.

The International AIDS Conference in Vienna heard today that a study of 400 HIV-negative men found that they were not more likely to take part in risky sexual behaviour when they believed the pills could prevent infection.

The small study gave half of the men a daily dose of Viread or a placebo immediately, while the other half were given the drug or a placebo nine months later.

Mitchell Warren, executive director of the New York-based AIDS Vaccine Advocacy Coalition, told Bloomberg News: “It is encouraging to hear there were no serious safety concerns and that the men in the study did not appear to increase risk-taking behaviors while taking a pill.

“Much more safety, adherence and risk data will be needed before PrEP [pre-exposure prophylaxis] can be implemented if it is proven effective.”

Seven of the 400 men became HIV-positive during the survey, although none of the men taking Viread did. Researchers said the study was not large enough to draw any conclusions about efficacy.

The US Centers for Disease Control and Prevention, which presented the research in Vienna today, say that PrEP is one of the most promising leads for tackling HIV and AIDS globally.

Earlier this week, the conference heard that a vaginal gel containing Viread was shown to reduce infections by 39 per cent in women in South Africa.