A study paid for by the U.S.’ National Institute of Allergy and Infectious Diseases, other U.S. government institutes and by GlaxoSmithKline PLC revealed that treating genital herpes with aciclovir, a generic antiviral medication, doesn’t reduce patients’ risk of being infected with HIV.

The study, published in the June 21 edition of The Lancet, found that people infected with the herpes simplex virus Type 2, or HSV-2, the most common cause of genital herpes, are almost three times more likely to become infected with HIV than those who don’t suffer from the disease. The findings showed that aciclovir reduced genital herpes by 47 percent and genital ulcers definitely linked to HSV-2 by 63 percent.

Aciclovir works by blocking an enzyme that allows the herpes virus to reproduce, stopping it to infect more cells in the body.

The study, involving 3,172 men and women in Africa, Peru and the U.S., also found that 75 people out of the 1,581 who had been receiving aciclovir were later infected with HIV, while, of the 1,591 people who received placebo pills, 64 contracted HIV. The women were also interviewed about their risky sexual behavior with their recent partners.

Connie Celum, a professor of global health and medicine at the University of Washington and lead author of the study said “it’s probably likely that we need considerably more potent interventions than we have,” the Associated Press reports.

This is the second study trying to suppress HSV-2 in order to protect against HIV with negative results. The first one was conducted in Tanzania earlier this year and was reported in the New England Journal of Medicine.