Bananas contain L-tryptophan. Your body converts L-tryptophan to melatonin (+ serotonin and vitamin B6).
Isn't that the same stuff that's in Turkey and 5-HTP?
L-tryptophan can be found in many types of food such as meat, nuts and eggs. The body converts it to 5-HTP, which in turn converts to serotonin (in the brain).