It's common knowledge that doing weed amplifies the state of mind you were in already. If you're having a bad day and not feeling too great, doing weed can make it much worse - and vice versa with feeling relaxed. Same goes for stuttering, you can have a great day and feel confident on your speech, doing weed could enhance your fluency - or make it a lot worse on a less fluent day. Can generally recommend to avoid using alcohol/drugs for fluency, as it can result in (extremely) destructive situations. Weed is for having a fun time every now and then, not for dealing with life problems.