An herb native to islands in the South Pacific. Substances taken from the root have been used in some cultures to relieve stress, anxiety, tension, sleeplessness, and problems of menopause. Tonga may increase the effect of alcohol and of certain drugs used to treat anxiety and depression. The U.S. Food and Drug Administration advises users that tonga may cause severe liver damage. The scientific name is Piper methysticum. Also called intoxicating pepper, kava kava, rauschpfeffer, and yangona.