He has opposed trials of the drug, he said, because of the likelihood that men would pursue the regimen on their own.
Other prevention experts worry about the sources of the drug. They believe some men are buying it online, raising questions of drug quality; others are getting it from HIV-positive friends, suggesting that those who are sharing doses aren't keeping up with their own treatment schedule. Some HIV-positive men are selling the drug to make extra money, Uhler said.
Albert Liu, director of HIV prevention and intervention studies at San Francisco's Department of Public Health, said the department planned to survey gay men early next year to see how many of them are using the drug before having sex.
If the numbers are as high as the CDC survey found, he said the department could begin educational campaigns about the drug's risks and widespread use.
"What we are trying to find out is if this is safe," Liu said. "Our goal is to find out what the best course of action is."
