An antiretroviral drug is showing promise in the fight to eliminate AIDS by drastically reducing the odds of contracting HIV when taken before and after sex.

According to a new study published by the New England Journal of Medicine on World AIDS Day Tuesday, study participants who took the antiretroviral drug Truvada prior to, and following sex were 86 per cent less likely to contact the virus compared to those who took a placebo.

The study looked at 400 gay men and transgender women at high-risk of HIV transmission. The high-risk group was defined as people who had unprotected anal sex with two or more different partners within a six-month period.

The study showed 14 of the 201 people in the placebo group developed HIV during the study-period, compared to two in the Truvada group of 199 people.

Participants were told to take two pills before sex, a third pill 24 hours after having sex, and a fourth pill 24 hours after that. When sexual intercourse happened more often, participants were told to take one pill per day and then the two post-exposure pills.

"Interestingly, participating in the study did not influence the participants' sexual behaviour," Dr. Cecile Tremblay of the University of Montreal, who led the Canadian component of the research, said in a news release.

All study participants received regular HIV and sexually transmitted disease prevention counselling, condoms and lubricant.

Tremblay said 28 per cent of the participants did not take the pills at all, and another 29 per cent did not take a high enough dose.

She also pointed out that the two people in the medication group who became infected had not medicated themselves.

Daily Truvada pills are already used to prevent HIV infection in people at high risk of infection, and studies have shown the drug helps even when some doses are skipped. However, taking the drug daily proved to be a challenge for some.

Researchers said the "as needed" strategy is designed to increase the likelihood that the patient would get the maximum benefit from the drug.

"Using antiretroviral therapy reduces the amount of virus in that person as much possible so they cannot transmit (HIV)," Robert Hogg of the BC Centre for Excellence in HIV/AIDS told CTV News Channel on Tuesday.

"That ultimately extends the lives of those individuals and reduces the number of new infections in that community.”