Of all the things humans rely on plants for-- sustenance, beauty, fragrance, flavor, fiber-- surely the most curious is our use of them is to change consciousness: to stimulate or calm, fiddle with or completely alter, the qualities of our mental experience. Pollan dives deep into three plant drugs-- opium, caffeine, and mescaline-- and explores the cultures that have grown up around these drugs. He examines the powerful human attraction to psychoactive...