(5-Hydroxytryptophan) Natural Source Supports Positive Mood Non-GMO A Dietary Supplement Vegetarian - Vegan How It Works: 5-HTP is the intermediate precursor in the natural synthesis of serotonin, a neurotransmitter that helps to regulate mood, appetite, and sleep/wake cycles. 5-HTP readily crosses the blood-brain barrier and clinical studies suggest that 5-HTP can support health serotonin levels. Serotonin is associated with positive mood and provides a substrate for the production of melatonin. 5-HTP is extracted from the bean of the African plant Griffonia simplicfolia, a natural vegetable source.