There's very little known about how party drugs interact with HIV medications. Why? Frankly, pharmaceutical companies aren't going to do this kind of research unless they get paid for it. And since the United States has a War on Drugs, it's pretty unlikely that Uncle Sam is going to spend money on it. Even if there was money for research, there are many other problems to overcome. For instance, the purity of party drugs varies greatly. It depends on who made them and what the ingredients were. Not to mention what the drugs were cut with. This is a reality of the drug market. Since there's no way of finding a consistent supply of "pure" party drugs, it's going to be hard to conduct any research that will truly reflect what might happen in the real world.
So, here's the dilemma. We don't know all of the potential harm and dangers of mixing HIV medications with party drugs. But we do know that bad things can happen when these drugs are mixed. Back in 1997 in England, a man with AIDS died suddenly after taking ecstasy (MDMA). This man was being treated for HIV with a protease inhibitor called Ritonavir. Ritonavir can have a "multiplying effect on drugs like MDMA. His friends said that he had only taken 2 tablets of ecstasy. But his blood levels measured 4.6 mg of MDMA. That's about 22 hits of ecstasy. Definitely not the fun night of dancing that he was hoping for.