5-HTP is an amino acid that your body produces naturally. Your body uses it to make serotonin, a chemical messenger that sends signals between your nerve cells. Low serotonin levels are associated with depression, anxiety, sleep disorders, weight gain and other health problems. That’s why supplements with serotonin-producing 5-HTP have become increasingly popular: 5-HTP can increase satiety, which means you eat less and lose weight. 5-HTP supplements increase serotonin levels in the body, which can improve symptoms of depression.