Lunesta is a controlled substance. It is a class 4 controlled substance. High doses of it in studies were shown to have similar euphoric effects at high doses similar to valium. At normal doses, it probably doesn't normally have this effect....but I would think that it should be used very very carefully in the addict because it is very similar to many sedative type medications that are abused.
Perhaps he could ask his doctor about something like Rozerem. This is a prescription sleep medication that works through melatonin receptors. Completely separate from most other prescription sleep medications which are sedative like medications.