Stimulant medications like Adderall work by increasing prefrontal cortex activity, which acts as a 'brake' on dopamine pathways, reducing impulsivity.

“The drugs that are normally given to treat those conditions ADHD and ADD are things like Adderall things that have very amphetamine, light qualities and structures, and you might ask, why would they do that? Well, it turns out that in kids these activate that for brain circuitry the break that exists on the deeper mesolimbic circuitry. So as you recall, there's the VTA and nucleus accumbens as the kind of accelerators on dopamine. And then there's the prefrontal cortex which acts as a break and can limit impulsivity. And those drugs tend to increase the activity of neurons in that pathway, the prefrontal cortex and it reduces impulsivity.”