NEW DELHI: The same drug used for treating HIV can also prevent gay and bi-sexual men from getting infected in the first place.In a landmark study, announced on Tuesday, scientists have found that Truvada -- a single daily pill containing two drugs that is being used by HIV patients -- actually reduces the risk of contracting the virus by at least 44%.In what is being hailed as the biggest success in finding a prevention tool against the deadly HIV, the iPrEx study -- published in the New England Journal of Medicine (NEJM) -- found that those, who popped the pill more than 90% of the time, were 73% less susceptible to contract HIV.The study, which involved nearly 2500 high-risk gay men, is significant because it gives credence to an HIV prevention approach called oral pre-exposure prophylaxis (PrEP), which involves the use of anti-retrovirals (ART) by those who are HIV-negative and at high risk of infection.The findings come only a few months after an African study by the Microbicide Trials Network (MTN) showed that a microbicidal gel can help protect women from contracting the virus."iPrEx has proved the concept of oral PrEP, and now its up to the field to build on this success and work towards realising the full potential of this promising approach in different at-risk populations, such as injection drug users and women. I am now convinced that there will be a day when we have several safe and effective methods for preventing HIV," said Sharon Hillier , professor and director of reproductive infectious disease research at the University of Pittsburgh School of Medicine.The iPrEx study involved 2,499 participants from Peru, Ecuador, Brazil, the US, South Africa and Thailand who were randomly assigned to one of two study groups: Truvada (a combination of tenofovir and emtricitabine) or Placebo. All participants received safe sex counselling and free condoms, and were tested for HIV and other sexually transmitted infections (STIs) during their monthly visit right through the programme.Of the 1,248 participants assigned to the Placebo group, 64 acquired HIV during the study as compared to 36 of the 1,251 in the Truvada group."The findings of this study have immense implications for the entire HIV prevention field, but most notably for global efforts focused on the population of men who have sex with men engaging in unprotected receptive anal intercourse," said MTN investigator Ian McGowan What about the concerns that people who take PrEP could develop drug resistance if they become infected with HIV?The researchers said, if someone became infected with HIV while using an ARV-based prevention strategy, then the patient's virus would be exposed to whatever ARV drug or drugs are being administered. Consequently, resistance to that drug could emerge.