Social Environment Impacts the Reward Pathway
Just as food gives us a jolt of pleasure by firing up the brain's reward pathway, so do our social interactions and environmental circumstances. If you have a great job, pleasant relationships, and are respected by your co-workers, you're going to feel prettygood. On the other hand, if you're bored with your job, have troubled relationships, and aren't respected by your co-workers, your reward pathway isn't getting much stimulation.
Individuals who don't receive enough natural rewards from their social environments are more likely to stimulate their neglected reward pathways with drugs.