Smoking weed is essentially just putting chemicals into your body. And everyone reacts differently based on their own chemical balances as well as tolerances. I could defiantly see how smoking weed can help people in MMA/BJJ/Etc. As for me it tends to not work. However, other drugs have helped with certain aspects of my game.
For example: I smoked before class one time and basically I didn't want to do anything. Drilling was fine but rolling sucked. I just didn't want to do it or be that physical. So... weed did not work for me.
However, I'm diagnosed with Panic Disorder and sometimes I get panic attacks and have to take Xanax. Unfortunatly, I sometimes have to take the pills close to when I have to go to class so I can't help but be a little bit loopy still when I show up. I've noticed that when taking Xanax and then rolling I am able to stay much calmer in bad situations and my game changes into a very strategic almost chess like form (Which is kind of silly because Xanax is supposed to shut off your brain). When I am not on it I tend to react much more instinctually without thinking as much.
Lately I've been trying to turn my game into much more of a thinking game regardless of whether I am on something or not and it's working. Proving (to me at least) that drugs can help your game but not in a way that cannot be achieved through a normal sober mind. The drugs may be able to make it easier to do certain things but if you set your mind to it you should be able to do it regardless of mindset (it may just take more practice).