Dude same here! I have myoclonus and caffeine and nicotine give me speech activated myoclonus that is indistinguishable from a stutter. Literally feels like my mouth can't articulate what my mind is trying to say. Benzos and alcohol have always made my myoclonus largely go away, and since it seems to be dopaminergic drugs that cause this it seems to me that drugs that increase dopamine whether by large release or reuptake inhibition are the cause.