A clinical trial to test a controversial pill for HIV prevention is set to begin in Toronto to determine how well it works in the real world, raising both hope and some concerns.

Truvada was originally marketed as a treatment for HIV infection. In 2012, the U.S. approved the daily pill as a preventive measure for healthy people who are at high risk of contracting HIV, including gay and bisexual men and heterosexual couples with one HIV-positive partner.

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Truvada can be taken to both prevent and treat HIV infection.

Dr. Darrell Tan, a clinician scientist in infectious diseases at St. Michael's Hospital in Toronto, is focusing on a pilot demonstration to test how well Truvada works as pre-exposure prophylaxis among gay and bisexual men who will be followed for one year.

He hopes the pilot will expand nationally.

On CBC Radio's The Current on Thursday, Tan pointed to five issues that come up in the field:

  • The prescription medication is used by people who by definition don’t have disease, which raises questions about its risk, benefits and how well it's tolerated.
  • Cost of about $900 a month.
  • Clinical and public health concerns about how it could potentially increase drug-resistance.
  • A theoretical risk that people might take more risks, either intentionally or subconsciously, in response to feeling protected against HIV.
  • The challenge of taking medication every day as prescribed, which research shows is the key predictor of how well it works.

Len Tooley of Toronto takes Truvada to help prevent HIV. He’s a co-ordinator of community health promotions at  Canada's Source for HIV and HEP C Information, or CATIE, where he talks to other gay men about HIV testing.

Tooley said he’s noticed what the Public Health Agency of Canada’s data also points to — HIV infection rates and transmission rates among gay men haven’t declined significantly since the early 2000s.

"While condoms are a really great option — they can be very effective in preventing transmission and many people find them a really great solution — they're not necessarily working to solve all of the questions we have for the HIV epidemic," Tooley said.

Another clinical trial is underway in Montreal to test how effective pre-exposure prophylaxis​ is when taken on an interim basis instead of daily.