Pollan was just giving his opinions on the three drugs and his limited experiences with them, with the exception of caffeine, which he claims to have been addicted to.
Review of Barons of the Sea
It tells the story of how American clipper ships—the fastest ships on the ocean—made obscenely huge fortunes for their owners using money from the opium trade to buy luxury goods in China—silks, teas, and porcelain—and sell them in America.