I've tried several drugs (mostly recreational). Of all the drugs I've tried, I've noticed these seem to have some effect (probably just a placebo): cannabis, kava root, alprazolam (xanax). The latter two are different than the effects you get from alcohol or cannabis. They're really relaxing and it really removes the "tense" feeling you get when you talk, not necessarily something that prevents the stutter but it makes it feel better. That's so hard to explain in words. I do usually end up talking way more fluently after taking a xanax. I really would like to get a prescription for xanax, but I'd be afraid that I would abuse it so I decided not to.