I've been following various trials about the therapeutic use of psychedelics and would be very interested in how it could help people who stutter. I've used them in conjunction with emotional processing techniques that I learned in counselling to great effect, although having a professional at hand would have been welcome. Every bit of psychotherapeutic progress I've made has led to improved fluency, even when that was not the goal. Psychedelics can help facilitate that. How effective they'll be on their own, I'm not sure, but I would devour any study about it that I could find.