L-Tryptophan  Precursor of serotonin, melatonin and niacin  Strengthening psychology and improving the quality of sleep  Suitable for vegetarians and vegans  Gluten and lactose free  Now Tryptophan dietary supplement contains tryptophan (tryptophan), an essential amino acid and precursor of serotonin, melatonin, and niacin (vitamin B3).    Serotonin is a brain neurotransmitter and is considered by experts to be the "happiness chemical" as it increases feelings of joy and contentment. Melatonin is characterized as the sleep hormone.    Low levels of serotonin are involved in the onset of depression.