Tryptophan is an amino acid needed for normal growth in infants and for nitrogen balance in adults. It is an essential amino acid. This means your body cannot produce it, so you must get it from your diet.
Murray MT. 5-Hydroxytryptophan. In: Pizzorno JE, Murray MT, eds. Textbook of Natural Medicine. 4th ed. St Louis, MO: Elsevier Churchill Livingstone; 2013:chap 98.
United States Department of Health and Human Services; United States Department of Agriculture. 2015-2020 Dietary Guidelines for Americans. 8th ed. health.gov/dietaryguidelines/2015/guidelines/. Updated December 2015. Accessed April 17, 2018.