Tryptophan is one of the 20 biologically active amino acids. As we learned in proteins, amino acids are the "building blocks" of a protein. There are more than one-hundred different amino acids found in nature. However, the human only utilizes 20 of these amino acids, and tryptophan is one of these.

Tryptophan is an essential amino acid and it can be found in the protein component of many foods. Tryptophan can be metabolized into niacin if needed. This pathway isn't the most efficient, and many times the amount of tryptophan are needed for a smaller amount of niacin. Nevertheless, the metabolic pathway is there if needed.

Tryptophan can also be used in the human to synthesize melatonin when needed.

Tryptophan is also used in the synthesis of serotonin. Serotonin (also named 5-hydroxytryptamine) is produced and stored in several tissues of the human, such as the intestine, blood platelets (thrombocytes), and in the central nervous system. Serotonin can help to regulate blood pressure, respiration, and exerts an effect in the sleep-wake cycle. Foods high in tryptophan, such as pumpkin seeds and turkey, can cause relaxation and even sleep.