People around the world start each day with a cup (or two, or three) of coffee or tea, relying on caffeine to sharpen their minds. We usually don’t think of caffeine as a drug, or consider our daily use as an addiction, because it is a legal and socially acceptable substance. But what is a “drug?” And why, for example, is making tea from the leaves of a tea plant acceptable, but making tea from a seed head of an opium poppy a federal crime?

In This Is Your Mind on Plants, Michael Pollan dives deep into three plant drugs — opium, caffeine, and mescaline — and throws the fundamental strangeness, and arbitrariness, of our thinking about them into sharp relief. Exploring and participating in the cultures that have grown up around these drugs while consuming (or, in the case of caffeine, trying not to consume) them, Pollan reckons with the powerful human attraction to psychoactive plants. Why do we go to such great lengths to seek shifts in consciousness, only to fence that universal desire with laws, customs, and fraught feelings?