From what I understand is, an excess of dopamine levels in certain parts of the brain is implicated in stuttering. I'm surprised to see that some people have improved their stuttering from taking concerta, considering the fact that concerta (methylphenidate) is a dopamine reuptake inhibitor. What this means is dopamine stays longer in the synapse, effectively increasing the potency of dopamine in the brain. OP, do you have ADHD as well? The unfortunate thing is, science and medicine is not there (yet) where we can target a drug that affects only a certain part of the brain and not the other part. You might have to make a choice- treat ADHD and stutter a little worse or discontinue Concerta and see some improvement in your speech. From a personal perspective, I would recommend a person exhaust all other non-pharmacological options, simply because there isn't a cure for stuttering through medication use. A stutterer would need to be on the medication for life. If you still want to go on a medication, understand that they should be used as training wheels- to practice speech techniques, gain confidence, and slowly taper off the medication, if possible. Just my two cents :)