AbstractFresh leaves of the khat tree (Catha edulis Forsk.) are chewed for their euphoric properties in East Africa and parts of the Middle East, such as The Yemen. This review describes the history, cultivation and constituents of khat, and the social aspects of khat chewing in Yemen. The major pharmacologically active constituent of the fresh leaves is (−)‐S‐cathinone. The pharmacology of (−)‐S‐cathinone in the central nervous system and the peripheral effects are described. (−)‐S‐Cathinone is regarded as an amphetamine‐like sympathomimetic amine and this mechanism of action is discussed in relation to the central stimulant actions and the cardiovascular effects of increasing blood pressure and heart rate. The risk factors associated with khat chewing are described, with emphasis on the reported increased incidence of acute myocardial infarction. Copyright © 2002 John Wiley & Sons, Ltd.