Take a look at
http://www.hptn.org/
There are many many studies going on now with the PrEP drugs. Some involve a degree of financial compensation for the participants.
But the downside is, if they are learning about the 'new drugs', then they do not yet know the multitude of side effects, or second order effects of using them. It all sounds interesting, and will possibly lead to big profits for the drug company who develops a winner. However, like most things, the unknowns with early tests could also mean negative consequences no one yet can imagine. Caveat emptor.