Certain embodiments of the invention provide a composition comprising at least two compounds selected from the group consisting of dihydromethysticin, methysticin, dihydrokavain, kavain, desmethoxyyangonin and 11-methoxyyangonin, wherein the composition is substantially free of flavokawain B. Certain embodiments of the invention also provide a method for treating or preventing cancer in a mammal (e.g., a human) in need of such treatment comprising, administering to the mammal a carrier and a compound selected from the group consisting of dihydromethysticin, methysticin, dihydrokavain, kavain, desmethoxyyangonin and 11-methoxyyangonin, wherein the compound is substantially free of other kava extract components.
