Holmes core thing though is that he has an almost ADHD-esque craving for novelty and tolerance for risk taking. He also can't stand not actively working on things, and when he's not working is when he's depressed. He doesn't seem to know how to actually feel good, but he knows how to be useful, thus his penchant for productivity boosters like cocaine.
He's a great character, but I wouldn't over pathologize him according to today's understanding of mental health. Doyle was a physician and gave Holmes various traits similar to what he had seen in his patients.