While I haven’t taken stimulants the non-stimulant SNRI ADHD meds tend to alleviate my stuttering. In particular Intuniv, an andrenergic alpha 2a receptor agonist noticeably reduces my stuttering in loud and noisy environments, which is where my stuttering has always been the worst. Just looked it up and Kratom also acts an alpha 2a agonist, so maybe there is some connection there.