L-Tryptophan is an essential amino acid which improves mental stability. Many people found tryptophan to be a safe and reasonably effective sleep aid, probably due to its ability to increase brain levels of serotonin (a calming neurotransmitter when present in moderate levels) and/or melatonin (a sleep-inducing hormone secreted by the pineal gland in response to darkness or low light levels). Clinical research has shown mixed results with respect to tryptophan’s effectiveness as a sleep aid, especially in normal patients. Tryptophan has shown some effectiveness for treatment of a variety of other conditions typically associated with low serotonin levels in the brain. In particular, tryptophan has shown some promise as an antidepressant alone and as an “augmenter” of antidepressant drugs.