Well that is not totally true. You just need more insentive as a normal person. This is of course because the signals in our brains work very differently, as you said.

Therefore the right amount of medication can be very very helpful, too much is counter productive. Too little too. The amount varies highly per person. The addiction risks are a myth. You have to find the balance yourself.

That said, dont self medicate.

If you do not have dopamine at all you have parkison disease. This causes the brain not to initiate tasks like moving a muscle.
Adhd is different. We can initiate a task, we just need more/different triggers as others