People with a d h d have some kind of problem with their dopamin circuitary, and that low levels of dopamine are are correlated with high a dh d symptoms. The second reason people with a dhd reach for drugs is because they feel like the amount of high you get makes it super awesome when you get drunk. And i suspect that a lot of theeo,  of the reasons that people of a d hD use drugs is because it actually offers some element of self medication.