Catha edulis Forsk leaves (khat) are chewed daily by a high proportion of the adult population in Yemen for the mild stimulant effect. Cathinone is believed to be the main active ingredient in fresh khat leaves and is structurally related and pharmacologically similar to amphetamine. The habit of khat chewing is widespread with a deep-rooted sociocultural tradition in Yemen and as such poses a public health problem. The objective of this literature review was to examine studies on khat, particularly human studies, with special reference to its effect on the central nervous system, cardiovascular, digestive and genitourinary systems, oral-dental tissues, diabetes mellitus and cancer.