Weed, ganja, pot, flower, dope, grass, bud: marijuana has many names, but an even greater number of chemical constituents, from THC, the psychoactive component, to cannabidiols such as CBD, often touted for its therapeutic potential. In this episode, Dr. Staci Gruber, an associate professor of psychiatry at Harvard Medical School who directs the longest-running study of medical cannabis use in the United States, discusses the effects of the plant’s components on human health. At a time when access to marijuana is progressively legalized, Gruber lays out the surprising ways in which its cognitive effects differ between youths and adults, and between medical marijuana patients and those who use the drug recreationally.