First, a few things. Many in my family are scientists, or drug policy activists, so I have learned about the science of Marijuana. That being said, while marijuana has been shown to physically alter the brain at any age, it has not been proven to have any negative performance effects long term. It's worth noting that short-term, especially before age 25, it reduces memory performance.
Please, don't make this post anything other than playing chess high. Obviously, I can't stop you, but if you'd like to talk about that start another post.
I know that this seems like an innapropriate, abusrd topic for this website, but I'd like to know other people's opinions on the subject.
I find that while I'm obviously a more stupid person stoned, I can play at the same level while stoned. I usually need to play longer games, because I tend to have more trouble doing any type of deep thinking, but I tend to see good moves more often, and threats from my opponent more. I win about as often while stoned or not stoned....