Yea I'm a habitual weed smoker and it definitely doesn't help my speech, but downers like alcohol or lorazepam slightly help with the anxiety part of the impediment. It is very complex all the elements that affect a persons stutter or speech in general. I feel like when I am on some kind of stimulant or smokin weed(pretty sure it's a stimulant, but not sure) I become hyper-aware, self awareness and situational awareness to the max, I notice everything, everyone, a fucking star comes into sight through the clouds and I see it. Maybe stimulants have the opposite effect on you?