Of course, the effect is not at all as intense as alcohol or other drugs, but there are effects. There are also, to my knowledge, some indications, that a lot of people with ADHD use it to self-medicate, since it seems to affect them differently, like other drugs do, too.

Sounds plausible; nicotine is a stimulant by means of triggering the release of adrenaline, dopamine, and serotonin. That is pretty much what an ADHD brain lacks.