Nicotine is a stimulant: ADHD'ers are self-medicating and probably before they even know they have ADHD. It's not (primarily) because of a lack of impulse control.

Nicotine does stimulate the prefrontal cortex like adderall so self-medicating can play a role, but a lot of people with ADHD don’t get addicted to their medication. From what i’ve experienced, its the behavior that’s hard to quit. Not saying you’re wrong, just that I think the higher number of smokers is more due to the fact that quitting is harder because of the action of smoking, not because it acts similar to medication in some ways.

I'm diagnosed with ADHD and never had the impulse to take drugs.

I even forget to take my meds sometimes.

Addiction is uncontrolled and damaging repetition of the behavior after initiation not the initial initiation itself