Khat is a shrub or small tree (Catha edulis) that grows in the higher regions of Yemen and East Africa. The plant is called qat in Yemen, tschad in Ethiopia, and miraa in Kenya. Chewing the leaves, buds, and sprouts of khat releases a substance that acts as a stimulant. Khat leaves can be made into a tea, but chewing is the most common way to achieve the stimulating effects. A person chews each leaf thoroughly and swallows the juice. Fresh, young leaves produce the greatest effect.

In Yemen, people often get together to chew khat in social settings, much as people in the United States or Western countries gather at coffee houses or in pubs for a beer. Use of khat is an important tradition and an essential part of a successful social life. In Yemen, many houses have a room set aside for the khat session...