Asklemmy

Everything, but mostly that it gets its name based on what annoys others instead of what bothers us. Attention problems and Hiperactivity are just two tiny parts of ADHD. There are other much more significant symptoms

In general the disorder is related to not properly processing neurotransmitters so everything that is "managed" by neurotransmitters can be out of whack. And some folks seem to have more problems with one kind of neurotransmitters than others.

Neurotransmitters are things like Dopamine, Serotonin, Endorfine, Noradrenalin. Example of stuff that are managed by them: Movement, control of the body, stress, sleep, attention, memory, learning, inhibition, joy, pain relief.

So, just by that you can probably imagine how broad the effects of ADHD might be.

We still don't know any way to treat the root cause effectively (neurotransmitters being "killed"). The only thing that helps, is forcing the body to generate more of those neurotransmitters, hoping that it'll process more of them that way. That works even with different stuff. If we generate more Dopamine, the body ends up processing more of the Serotonin it already produces too. That's why stimulants work so well at regulating us - it floods our brain with artificial stuff that end up "shielding" the natural stuff to let them do their job too.

That is also why stimulants can sometimes make us more relaxed or even sleepy - it's not that the stimulant itself causes that, but it let's the body finally process everything properly so it can understand that it is supposed to be sleepy.

For someone without ADHD where the neurotransmitters are processed properly, stimulants will do nothing more than stimulate.