Supports healthy serotonin levels in the brain to help balance appetite, mood, and sleep. 5-HTP (5-hydroxytryptophan) is a precursor to serotonin, an important neurotransmitter in the brain that is involved in mood regulation, appetite control, and sleep. 5-HTP is a safe alternative to L-tryptophan, that supports serotonin and melatonin levels while allowing your body to self-regulate these neurohormones.