I was reminded of an experiment that several of the addiction researchers I interviewed had told me about — the so-called rat park experiment. It’s well known in the field of drug abuse research that rats in a cage given access to drugs of various kinds will quickly addict themselves, pressing little levers for the drug on offer in preference to food, often to the point of death. Much less well known, however, is the fact that if the cage is “enriched” with opportunities for play, interaction with other rats, and exposure to nature, the same rats will utterly ignore the drugs and so never become addicted. The rat park experiments lend support to the idea that the propensity to addiction might have less to do with genes or chemistry than with one’s personal history and environment.

—Michael Pollan, How to Change Your Mind, Allen Lane, 2018