Botanical name: 

Several species of lactuca, native to the Old World, yield the juice which, when dried, is known as Lactucarium, an extract known also under the name Lettuce Opium. The fact that lettuce eaten frequently induces drowsiness, was known in ancient times, and its reputation in this direction led Dr. Coxe (171), of Philadelphia, to suggest the collecting of the juice, after the manner employed in the making of opium. His experiments were published in 1799 under the title "Lettuce Opium." Since that date others writing on the subject created quite a demand for the lactucarium thus produced. It will be seen that the introduction of this substance to medicine came through usual empirical channels.

The History of the Vegetable Drugs of the U.S.P., 1911, was written by John Uri Lloyd.