Is dopamine responsible of adhd ? and does it have a relation to happiness ? and serotinin ?

Library in a capsule: Yes, low Dopamine is thought to be related to (not responsible for) adhd - it's complicated. No direct relation to mood but since the effects are problems, i imagine they make a person unhappy. Serotonin is also very complex in action, but it is somewhat the opposite i.e., not a big role in conditions like adhd but a major one in mood regulation (which is a bit different from "happiness") best!