Hey man, This totally makes sense. The research shows that stuttering is associated with elevated sympathetic (fight or flight) nervous system and that involves elevated release of adrenaline. Propranolol blocks adrenaline receptors, which inhibits adrenaline. This allows the parasympathetic (rest & digest) nervous system to predominate. It's also been shown to slightly decrease dopamine too. Elevated dopamine is another mechanism related to stuttering.