L-tryptophan is an essential amino acid; like vitamins and minerals, tryptophan can't be made by the body and must come from the diet. Among the many functions of tryptophan is producing the brain neurotransmitter serotonin. Serotonin influences mood, relaxation, sleep and appetite. Many people see improvements in these areas when they use nutrients to increase serotonin such as l-tryptophan or 5-HTP. Although there is some tryptophan in protein foods, it's the least abundant amino acid in the diet, so taking extra tryptophan may improve serotonin production with a positive effect on mood, sleep and appetite regulation. Tryptophan may also enhance HGH production during sleep. Source Naturals is an ideal L-tryptophan supplement to use, with the preferred 500 mg potency. Take on an empty stomach before bedtime for best results.