What is 5-HTP? 5-HTP is an herbal supplement, derived from the herb Griffonia simplicifolia. In the body, 5-HTP (5-hydroxytryptophan) gets converted to the neurotransmitter serotonin. Serotonin has an enormous influence on how we feel physically and mentally, but since serotonin can't be supplemented directly, people use 5-HTP for help with a wide range of conditions related to low serotonin levels, primarily appetite regulation, poor mood, and poor sleep patterns. NOW Foods is a best-selling brand of 5-HTP which is available in 50 and 100 mg. potencies.