There is also concern that the high cost of Truvada could divert limited funding from more cost-effective options.
"We need to slow down. I care too much about my community not to speak my concerns," said Joey Terrill, of the Aids Healthcare Foundation, which campaigned against the drug's approval.
Nurse Karen Haughey told the panel: "Truvada needs to be taken every day, 100% of the time, and my experience as a registered nurse tells me that won't happen.
"In my eight years, not one patient that I've cared for has been 100% adherent."
But others welcomed the panel's recommendation.
"This brings us closer to a watershed for global HIV prevention efforts," said Mitchell Warren, executive director of the Aids Vaccine Advocacy Coalition, after the vote.
The FDA is expected to make its decision by 15 June.
In the UK, Sir Nick Partridge, chief executive of Terrence Higgins Trust, said: "There is no single method of prevention that can on its own stop the transmission of HIV.
How One Can Try Not to Become HIV-Infected
HIV can enter one's body by several different routes: indirectly through eye, oral, anal, vaginal, or urethral (female/male urine canal) contact, and directly through the bloodstream via any opening in the skin. The walls of all tissue (the eye, upper and lower respiratory, genital, urethral, intestinal) except the skin, which are exposed to the environment are lined with mucosal tissue.