Dietary supplement. L-5-Hydroxytryptophan supports normal sleep cycles. 5-HP (L-5-Hydroxytryptophan) is an intermediate in the natural conversion of the essential amino acid, tryptophan, to serotonin. Clinical studies have shown that 5-HTP increases the amount and availability of serotonin produced by the body. Increased brain serotonin levels may produce positive effects on emotional well-being, appetite regulation, melatonin production and maintaining a healthy sleep cycle.