5-HTP (5-hydroxytryptophan) is a naturally-occurring metabolite of the essential amino acid tryptophan. 5-HTP for use in dietary supplements is derived from the seeds of the Griffonia simplicifolia plant. Additional Information: Metabolism and absorption of 5-HTP 5-HTP (5-hydroxytryptophan) is formed by the addition of a hydroxyl group (-OH) to the 5 carbon of the indole ring of tryptophan. Conversion of tryptophan to 5-hydroxytryptophan is catalyzed by the enzyme tryptophan hydroxylase.1 5-HTP functions as the precursor for serotonin, and is converted to serotonin in a pyridoxal phosphate (vitamin B6) dependent reaction catalyzed by the enzyme L-amino acid decarboxylase.2 - Synthesis of serotonin in the brain requires an adequate supply of either tryptophan or 5-HTP as precursors. The supply of tryptophan available for conversion to 5-HTP depends on a number of factors, including nutritional status and competition between tryptophan and other amino acids for transport across the blood brain barrier. - Disturbances in the serotonin metabolic pathway may disrupt central nervous system functions which utilize serotonin as a neurotransmitter.2 Administration of 5-HTP bypasses the conversion of tryptophan to 5-HTP. 5-HTP readily crosses the blood brain barrier and becomes available for serotonin synthesis. Serotonergic neurons (nerve cells stimulated by serotonin) regulate sleep, appetite, nociception (the perception of pain), and aggressive behavior.2 - Serotonin is metabolized to 5-HIAA (5-hydroxyindolacetic acid) which is its primary breakdown product.3 The concentration of 5-HIAA in cerebrospinal fluid is used as an indicator of serotonin turnover in the CNS serotonin level. Psychiatric patients have been found to have low levels of 5-HIAA in the CNS fluid, suggesting serotonin deficiency.3 - 5-HTP is readily absorbed by the mucosal cells of the gastrointestinal tract. In one study using five subjects, systemic absorption of 5-HTP in combination with carbidopa averaged 69.2 percent.4 Another absorption study found that carbidopa enhanced the increase in serum 5-HTP concentration 5 to 15 fold.5 In this study, a single dose of 5-HTP increased the plasma level of 5-HTP only slightly, whereas 5-HIAA increased 9-20 fold. This suggests that the gut mucosa has a storage capacity for 5-HTP, and that plasma increases occur after maximum capacity is reached.5