@kylacanzater
Lettuce has a natural compound Lactucopicrin and lactucin that has been used historically as a sedative, and can serve as a sleep aid. Here are the lettuce with the highest levels of this compound...
Romaine lettuce has the highest levels of lactucin (361.50 mg) and 226 mg of Lactucopicrrin.
Green Romaine lettuce is easier to find and contains more lactucin (1071.67 mg) and 150 mg of Lactucopicrin.
Green lettuce has a high level of lactucin (446 mg) coming in third place.