There is some scientific evidence that people who stutter have excessive dopamine in certain regions of their brain and this might play a role in their stuttering. A dopamine antagonist like Haloperidol lowers the dopamine level in the brains and can make you stutter less. It however comes with some very severe side effects, I'm not sure if its worth it. How are you so certain your stuttering is purely psychological and not neurological? Have you made a MRI of your brain to rule that out?