AIDS prevention has been on a sort of rollercoaster in the past year or so, with exciting progress followed quickly by disappointing results. The drug Truvada showed promise in blocking transmission of the virus, but then an African trial had to be stopped because the drug wasn't protecting the women who took it. Now, however, it looks like there may be an explanation — some of the women in the trial weren't actually taking the drug. Scientists aren't sure why, but they did note that AIDS is heavily stigmatized, and having a bottle of AIDS drugs in your house might make other people think you're infected — even if you're actually taking the drugs prophylactically. This is good news for Truvada, but somewhat bad news for the fight against AIDS. It's a reminder that even if scientists find effective drug treatments, they may need to clear social hurdles as well.