First documented in the Divine Farmer’s Materia Medica Classic of the first or second century, the bark of the mimosa tree, known as he huan pi (“collective happiness bark”), is thought to harmonize the emotions and render a person worry-free. The manual advises that “protracted taking may make the body light, brighten the eyes,” and induce one to feel “as if one had acquired whatever one desired.” Modern practitioners sometimes call it “herbal Prozac.”