Depression and serotonin metabolism: rationale for neurotransmitter precursor treatment.

The authors review evidence suggesting that some depressed patients have disturbances in serotonin metabolism. Research supporting the serotonin hypothesis includes: cerebrospinal fluid studies; postmortem examination of neurotransmitters, their metabolites, and their receptors; platelet studies; neuropharmacologic data; neuroendocrine perturbations; and reports that serotonin precursor compounds (tryptophan and 5-hydroxytryptophan) may benefit some depressed patients. The authors conclude that better designed studies are needed to test whether serotonin precursor compounds have antidepressant properties.