Drugs don't really make people happy. Happiness must come from within.
The Happy life is thought to be one of excellence; now an excellent life requires exertion, and does not consist in amusement. If Eudaimonia, or happiness, is activity in accordance with excellence, it is reasonable that it should be in accordance with the highest excellence; and this will be that of the best thing in us.
-- Aristotle, "Nichomachean Ethics"
What I get out of that, is that people are happy when they have a sense of purpose and feel like they're doing "what they need to do". Of course, sometimes that is very bad for everyone else. But think about what happened to that guy from Fight Club, who was working at the convenience store but wanted to be a veterinarian.