Lactucarium n. : The inspissated juice of the common lettuce, sometimes used as a substitute for opium.

Example:
How to extract Lactucarium from lactuca sativa(lettuce)?

Taxonomy
Lactucarium, lettuce opium, 2007-05-28, Lactuca virosa, free encyclopedia, lettuce, analgesic, Plants, latex, Lactuca, the seeds, milky fluid, seeds, alkaloid, lozenges, syrups, Lactuca sativa, compounds.

Defination from the web:
Lactucarium is the milky fluid secreted by several species of lettuce, especially Lactuca virosa, usually from the base of the stems. Lactucarium is known as lettuce opium because of its sedative and analgesic properties. ...