Does drug usage have a genetic component or is drug usage environmentally induced?

This is the age old question of nature vs. nurture. There are arguments for both sides. The genetic component of overuse of any substance (drugs, alcohol, food etc.) has been linked to how people's brains work. I have heard that the pleasure center is what controls our thinking about what we need. To some extent, seritonin levels are affected by what we ingest and people tend to self-medicate to make themselves feel right. An argument for nurture is that the way you were raised from babyhood on has an effect. Or that your experience in society affects your choices.