Rat Park is a famous study in which lab rats were kept in a really nice habitat that satisfied their every need. Contrary to the usual results with lab animals, scientists couldn't get these happier rats addicted to drugs. Researchers concluded that drug addiction, far from being the simple biological story everyone assumed it was, was really a just coping mechanism for intolerable social situations. Rats stuck in terrible cages get addicted to drugs, as do humans in terrible slums. But give them other opportunities for happiness, and the problem disappears.

This has since turned into popular legend. From HuffPo: The Likely Cause Of Addiction Has Been Discovered, And It Is Not What You Think. From Intellihub: Rat Park Heroin Experiment Shows Cultural Roots Of Drug Addiction. There's even a Rat Park Comic and the inevitable Trump Could Learn From The Rat Park Experiment thinkpiece.