L-Tryptophan in Psychiatric Practice

Abstract

The amino acid L-tryptophan is being prescribed more and more for the treatment of depression. Since L-tryptophan is a precursor to serotonin and crosses the blood brain barrier, it is believed by some investigators to be most effective in depressions secondary to serotonin deficiency. Several studies using L-tryptophan with and without concomitant tryptophan pyrrolase inhibitors, decarboxylase and hydroxylase cofactors, or decarboxylase inhibitors, have indicated its usefulness in combatting depression, but other studies have found it to be of value only as an ancillary drug therapy with tricyclic antidepressants and especially with monoamine oxidase inhibitors. The drug's sedative side effect has prompted several studies which indicate it has some value as a hypnotic agent. L-tryptophan has also been reported to be useful in acute mania, although its mechanism of action in this condition is not well understood. Side effects to L-tryptophan use are minimal, but long-term adverse effects are in question, as certain tryptophan metabolites have been implicated as being in excess in bladder and breast cancers. The greatest utility of L-tryptophan is probably as a concomitant agent with MAO inhibitors, and in depressions that have not responded to tricyclic antidepressants, MAO inhibitors alone, or electroconvulsive therapy.