The essential amino acid l-tryptophan is a serotonin precursor. Research indicates that l-tryptophan supplementation may support emotional well-being and restful sleep. In a double-blind, placebo-controlled study, l-tryptophan supported healthy emotional processing and promoted positive outlook in women. In a separate study, it supported healthy mood and lessened occasional irritability during the menstrual cycle. l-Tryptophan also supports healthy sleep quality, onset and duration. Additional research suggests that tryptophan may promote relaxation and help control occasional cravings. Vitamin B6 provides enhanced support as an important cofactor involved in the metabolism of l-tryptophan.