L-5 Hydroxytryptophan. Supports Normal Sleep Cycles. 5-HTP (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 of emotional well-being appetite regulation melatonin production and maintaining a healthy sleep cycle. Source Naturals 5-HTP is naturally derived from the seeds of the African plant Griffonia simplicifolia.