It's definitely not a performance enhancer, but it's against the rules so what are you gonna do, you know?
If you listen to Diaz talk about weed on the Beatdown, he actually says that it enhances his performance. He claims that it helps him kick back after training or something, there's no way he's not high in that interview, he's going off about the wonders of organic foods and how the government is on some conspiracy **** about kids and ritalin. Then he goes off on tangents and has to ask what he was talking about...classic stuff.