This 1998 review by Timothy C. Birdsall, N.D., explores the clinical efficacy of 5-hydroxytryptophan (5-HTP) as a serotonin precursor. 5-HTP, derived from L-tryptophan or extracted from Griffonia simplicifolia seeds, bypasses the rate-limiting step of serotonin synthesis and crosses the blood-brain barrier without a transport molecule. It is well absorbed orally,
