Serotonin is a hormone and neurotransmitter that helps stabilize our mood, feelings of well being, and happiness. Serotonin is made from an amino acid called tryptophan. The amino acid is found in foods such as nuts, cheese, and red meats. In humans, serotonin is primarily found in the nervous system and digestive system. It enables brain cells and other nervous system cells to communicate with each other. Having high levels of serotonin is thought to increase happiness, regulate anxiety, and heal wounds. Low levels of serotonin can lead to mood disorders such as anxiety and depression.