Interesting you say that! I remember in my younger years doing MDMA my stutter completely disappeared. I never felt so free speaking. It was life changing, but the crash the next day made my stutter temporarily worse. In researching this, I realised MDMA helped because it causes a sudden surge of seratonin in the brain, which essentially calms the brain from a hyperactive dopaminergic system. When that effect wears off, dopamine returns to its overactive state, and we lose control of our speech motor pathways and stuttering returns.