Press Release

Preliminary Safety and Adherence Data from Oral PrEP Trial Released; Trial Not Designed to Evaluate Effectiveness

New York, NY – Preliminary data were presented today at the International AIDS Conference by the US Centers for Disease Control and Prevention (CDC) from a safety and acceptability trial of daily use of oral tenofovir in HIV-negative gay men and other men who have sex with men (MSM) in the United States. These data, which do not include any evaluation of PrEP effectiveness, add to the body of information about ARV-based prevention available to researchers, policy makers, community and other stakeholders.

This trial, known as CDC 4323, is one of several trials around the world testing the use of antiretroviral drugs to prevent HIV infection, a concept known as PrEP, or pre-exposure prophylaxis.

The findings presented today showed that no serious safety concerns emerged in the initial analyses. CDC also shared early findings about risk-taking among men in the study. The trial was designed so that some men began taking the daily oral tenofovir or a placebo pill immediately, while other participants were delayed by nine months. This design allowed the research team to gather information on how pill-taking affected sexual behavior in participants who were all receiving the same standard prevention package, including counseling about safe sex, condoms and STD testing for the duration of the trial. The preliminary analyses indicate that rates of risk behaviors were comparable between the participants randomized to begin taking tenofovir or placebo pills daily immediately compared to those who began after nine months of trial participation.

Importantly, these results did not provide any information on whether PrEP reduces the risk HIV infection. This trial focused solely on safety and behavior issues and was not designed to explore possible effectiveness of PrEP. Several studies that are studying possible PrEP effectiveness are currently underway.

“The information from this trial provides important pieces of information about the possible use of PrEP if it is proven effective in other ongoing effectiveness trials around the world,” said Mitchell Warren, AVAC executive director. “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.”

“But much more safety, adherence and risk data will be needed before PrEP can be implemented if it is proven effective. And, importantly, this trial does not tell us anything about whether or not PrEP will work to reduce the risk of infection,” Warren added.

“Antiretroviral-based prevention research shows great promises, especially in the light of the positive results from the CAPRISA 004 microbicide proof-of-concept study released earlier this week. Although the CDC safety study used oral tenofovir, the same antiretroviral that was formulated as a gel in the CAPRISA 004 microbicide study, it is important not to extrapolate between the two studies. There are a series of ongoing trials that still need to be completed before we know whether PrEP can be added to our list of available HIV prevention options. Each of these trials provides a piece of the puzzle of how antiretrovirals might be used by HIV-negative people to reduce their risk of acquiring HIV,” Warren said.

More information about PrEP research is available in AVAC’s publication A Cascade of Hope and Questions: Anticipating results of ARV-based HIV prevention trials, available at

Mitchell Warren, +1-914-661-1536,

Kay Marshall, +1-347-249-6375,