Tryptophan is one of the essential amino acids that must be included in the human diet because the body cannot produce it on its own. It is crucial for a number of metabolic functions, but one particular function has caught the attention of scientists because it may improve mood and cognitive abilities. Tryptophan is a building block for serotonin in the brain, and serotonin is a known as the happiness hormone. Many studies have now found that taking tryptophan can be an effective way to reduce anxiety and increase positive mood (1, 2, 3, 4).