Mood effects of the amino acids tryptophan and tyrosine
Acta Psychiatrica Scandinavica, 04/21/2011
Clinical Article
Parker G et al. – Acute tryptophan depletion continues to provide a research tool for investigating the relevance of serotonin to depression onset. There is limited evidence that tryptophan loading is effective as a treatment for depression through its action of increasing serotonin production. Most clinical studies are dated, involve small sample sizes and/or were not placebo controlled. The development of the new serotonin reuptake inhibitor drugs seemingly signalled an end to pursuing such means of promoting increased serotonin as a treatment for depression. The evidence for tyrosine loading promoting catecholamine production as a possible treatment for depression appears even less promising, and depletion studies less informative.
Methods- Theoretical relevance of 2 amino acids overviewed by considering published risk and intervention studies, technical papers and reviews
- Some limited evidence, suggesting that depressed patients, especially those with melancholic depression, have decreased tryptophan levels
- Whether such findings reflect causal contribution or are aconsequence of depressed state remains open question
- Small database supporting tryptophan preparations as benefitting depressed mood states
- No clear evidence as to whether tyrosine deficiency contributes to depression
- Only randomized double-blind study examining tyrosine supplementation did not show antidepressant benefit
