Lactuca virosa is a plant in the Lactuca (lettuce) genus, ingested often for its mild psychotropic (specifically hypnotic or sedative) effects which are often described as being similar to those of opium. It is related to common lettuce (L. sativa), and is often called wild lettuce, bitter lettuce, laitue vireuse, opium lettuce, poisonous lettuce, tall lettuce, great lettuce or rakutu-karyumu-so.
Lactuca virosa is widespread across much of central and southern Europe. It can be found locally in the south east and east of England. In the rest of Great Britain it is very rare, and in Ireland it is absent. It is also found in the Punjab Region of Pakistan India and Australia where it grows in the wild.
Lactuca virosa was used in the 19th century by physicians when opium could not be obtained. It was studied extensively by the Council of the Pharmaceutical Society of Great Britain in 1911. They discovered two chemicals responsible for the properties of L. virosa; lactucopicrin and lactucin. In the United States, the plant experienced a resurgence in popularity in the 1970s. Today the plant is un-scheduled by the Food and Drug Administration (FDA), meaning it is legal to grow, purchase and own without prescription or license.