Well, it is believed that stuttering is caused by an overall dopamine dysfunction.  In some regions of the brain, dopamine may be too high and in others, too low. So it´s not that simple, you can have parkinson (low dopamine) and stuttering, antipsychotics (dopamine antagonists) usually decreases stuttering but sometimes they don´t, and even if it´s not a very low dosage, it can worsen stuttering. There are drugs that decrease stuttering in some persons and increase it in others, and quite a few people get benefit with dopamine AGONISTS (methylphenidate for example, usually improves the condition and is a dopamine agonist). This is called the dopamine paradox. There is a lot of double blind placebo studies of dopamine acting drugs that decrease stuttering. But no one is approved to treat the condition. Anyway, some psychiatrists would accept to give you a prescription if you show him/her the study.