funny thing is I disagree with them when they say marijuana isn't a performance enhancing drug. I smoke weed all the time and go to the gym and I can workout way harder and way longer when I'm high by a significant factor, it's easier to regulate your bodies rhythms and ignore the voice that tells you to quit when you are high so you can get more energy out.
It's why guys like Nick Diaz can train for triathlons, so I can definitely understand why it's a restricted drug. Put me in a fitness training contest with someone who doesn't smoke and I already have a huge advantage, it doesn't work like that for everyone but for some people it does and it creates an unfair advantage when it helps the person train. Some would say it wrecks your cardio and slows your mind, which isn't true if you are an active person. Weed tends to make some people lazy, but if it doesn't then it's unfair. Sure it wouldn't be best to smoke up before a fight because it can slow your reaction time, but in training it helps a lot.