This section is from the book "Botanic Drugs Their Materia Medica, Pharmacology and Therapeutics", by Thomas S. Blair. Also available from Amazon: Botanic Drugs, Their Materia Medica, Pharmacology and Therapeutics.
Lettuce, Lactuca virosa, is official in Hungary, Mexico, the Netherlands, Spain, and the U. S. Lactuca sativa is official in Mexico and Serbia. L. altissima is a suitable substitute for L. virosa; it is used by Aubergier, who has given the species comparative study.
A mild hypnotic said to contain traces of hyoscy-amine. Only the wild species of lettuce yield lactu-carium in any appreciable amount. The drug is an unreliable hypnotic, but 15-grain doses may be used as a substitute for opium, being effective in some cases. The average dose of the tincture is 30 minims. The syrup, in 1/2 to 2-drachm doses, is of some value in controlling irritable cough, more particularly in children.