If I smoke and am near a guitar, I'm usually forced to pick it up for a few minutes. Smoking helps my right hand relax since I changed my picking style about six months ago. On the other hand, my improv is a little slower and I can often get stuck in the same phrase. I'd say take a few hits. Loosen yourself up a bit because that's what good technique is all about.
I would think of it like anything else when smoking. Weed effects you in so many ways, it's like driving. I would never ride in the car with someone who is 1) not an experienced smoker and 2) who is not an experienced driver and finally 3) someone who does know how to do both at the same time. Now, I don't recomend that everyone drives and smokes it's not for everyone but you can't learn to do anything while stoned without practice. Now, going to a lesson stoned is not the best of ideas but I am sure I would love to grove along and play music while stoned.
I always loved playing my guitar while I was high, I just never really did anything to get any better. I loved playing around but I think its best to go to a lesson sober... Or at least coming down.
