People have been coexisting with plants for millions of years. Long before medicine, people were eating plants and taking note of which ones were useful for nutrition, medicine, or even for poison. Sometimes a plant could be all three of these things, depending on its preparation and consumption.

The ancients noticed that willow, poppy, and wild lettuce were useful for pain killing. Willow contains salicylic acid, used to make aspirin. Poppy contains morphine and other opiates. Sprouted lettuce contains a naturally occurring alkaloid called lactucin, which is found in the white milky sap of the plant. This is how it got its nickname, lettuce opium. Lettuce gets it's very name from the Latin word for milk, lactuca.

The word itself “opium”, comes from the Greek root “opos”, meaning juice. Lettuce opium would just mean lettuce juice, philologically evolving into the category of things poppy related, though it is not a poppy or morphine containing plant. Willow, poppy, and wild lettuce have their medicinal roots going back into prehistory, even mentioned by the ancient Sumerians. By the time ancient Egypt was flourishing, these plants were in full use.

Science can now tell us why wild lettuce works for pain killing, because it contains bitter compounds known as sesquiterpene lactones. All lettuces contains them, but wild lettuce contains them in higher quantities. The more bitter, the more of these active compounds are present.

These compounds have a pain killing and anti-inflammatory effect on the immune system, because they inhibit the NF-κB protein. This protein controls the cyclooxygenase-2 enzyme, also known as COX-2, an enzyme responsible for pain and inflammation. Other pain killers such as ibuprofen work in the same or similar fashion.