Original Investigations


, Volume 87, Issue 2, pp 173-177

First online:

Tryptophan depletion causes a rapid lowering of mood in normal males

  • Simon N. YoungAffiliated withDepartment of Psychiatry, McGill University
  • , Scott E. SmithAffiliated withDepartment of Psychology, McGill University
  • , Robert O. PihlAffiliated withDepartment of Psychiatry, McGill UniversityDepartment of Psychology, McGill University
  • , Frank R. ErvinAffiliated withDepartment of Psychiatry, McGill University

Rent the article at a discount

Rent now

* Final gross prices may vary according to local VAT.

Get Access


Normal male human subjects ingested amino acid mixtures which were tryptophan-free, balanced or contained excess tryptophan. The tryptophan-free mixture causes a marked depletion of plasma tryptophan by 5 h. At this time the subjects in the tryptophan-free group had significantly elevated scores on the depression scale of the Multiple Affect Adjective Checklist. The tryptophan-free group also performed worse than the other two groups in a proofreading task carried out while listening to a tape with themes of hopelessness and helplessness (dysphoric distractor). Cognitive theories of depression predict greater distractability of depressed individuals by dysphoric themes. Thus, both measures indicate a rapid mood lowering effect of tryptophan depletion in normal males. This effect is probably mediated by a lowering of brain 5-hydroxytryptamine. Although the mood-lowering effect was not as great as that seen in depressed patients, our results suggest that low brain 5HT might be one factor precipitating depression in some patients.

Key words

Tryptophan 5-Hydroxytryptamine Depression