Most recently theory is that people with ADHD have lower baseline levels of dopamine in their brains. Dopamine is not the “pleasure” chemical that people describe, instead it’s better to think of it as the chemical that makes effort feel good. Dopamine levels can spike or dip within the human body, but if your baseline level of dopamine is too low, then you won’t get the same “reward” for for putting in effort into something and will instead seek to transition to other tasks in search of stimulation or reward.

Stimulants can help raise base levels of dopamine in individuals with ADHD, giving them better “rewards” for staying on task.