L-Tryptophan, 500 mg 120 caps from Source NaturalsL Tryptophan Mood, Relaxation, Sleep L Tryptophan is a natural amino acid that is the precursor to serotonin and melatonin, which is a neurohormone that affects the bodys ability to sleep, relax and feel good. It plays a part in the synthesis of both melatonin and serotonin, hormones involved with mood and stress response. L Tryptophan also supports immune functions because it is the body's precursor to the kynurenines that regulate immunity. If