I am in really bad shape and have just started working out after a long time. I've lifted while stoned several times. I got the idea from Kevin Spacey in "American Beauty." Anyway, I seem to be gaining a ton more muscle than other times I've worked out regularly.

As long as you don't smoke so much (or have a high enough tolerance) that you don't get completely silly, you should be fine. (i.e., you don't want to get into a laughing fit in the middle of a rep).