Most seems to agree that it's related to the dopamine levels in the brain. https://en.wikipedia.org/wiki/Dopamine_hypothesis_of_stuttering There are studies where stuttering in successfully treated with dopamine antagonists, like olanzapine. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3678230/ Myself, I'm being treated successfully with olanzapine for stuttering. It's not gone, but a lot better.