Mood effects of the amino acids tryptophan and tyrosine: 'Food for Thought' III

Acta Psychiatr Scand. 2011 Dec;124(6):417-26. doi: 10.1111/j.1600-0447.2011.01706.x. Epub 2011 Apr 12.


Objective: Reflecting increased scientific interest in any nutritional contribution to the onset and treatment of mood disorders, we overview research into two neurotransmitter precursors - the amino acids tryptophan and tyrosine - particularly examining whether any deficiency increases risk to depression and whether those amino acids have any antidepressant properties.

Method: The theoretical relevance of the two amino acids was overviewed by considering published risk and intervention studies, technical papers and reviews.

Results: There is some limited evidence, suggesting that depressed patients, especially those with a melancholic depression, have decreased tryptophan levels. Whether such findings reflect a causal contribution or are a consequence of a depressed state remains an open question. There is a small database supporting tryptophan preparations as benefitting depressed mood states. There is no clear evidence as to whether tyrosine deficiency contributes to depression, while the only randomized double-blind study examining tyrosine supplementation did not show antidepressant benefit.

Conclusion: 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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • Antidepressive Agents / metabolism
  • Antidepressive Agents / pharmacokinetics
  • Biological Availability
  • Catecholamines / metabolism
  • Clinical Trials as Topic
  • Depression / metabolism*
  • Humans
  • Mood Disorders / metabolism*
  • Neurotransmitter Agents / metabolism
  • Nutritional Requirements
  • Serotonin / metabolism
  • Synaptic Transmission / drug effects*
  • Tryptophan* / metabolism
  • Tryptophan* / pharmacokinetics
  • Tryptophan* / therapeutic use
  • Tyrosine* / metabolism
  • Tyrosine* / pharmacokinetics
  • Tyrosine* / therapeutic use


  • Antidepressive Agents
  • Catecholamines
  • Neurotransmitter Agents
  • Serotonin
  • Tyrosine
  • Tryptophan