Current thinking is ADHD is caused (at least in significant part) by a lack of dopamine or an insensitivity to dopamine. They’ve found links between genes that cause dopamine resistance and ADHD.
Many current ADHD medications cause increased levels of dopamine. This is a leading theory on why they work.
Wanna guess what a lot of other drugs, including alcohol, do in your brain?
It’s been amazing since I got diagnosed relatively late in life exactly how many other things suddenly made so much more sense and clicked into place. And amazing how quickly decades old substance abuse habits started to taper off once my brain chemistry was less fucked.
Oh wait, that isn't fun at all.
ADHD is real and untreated it can (and often does) destroy lives.
(Also: People with untreated ADHD have 3x the gen-pop rate of car accidents!)