Effect of acute tryptophan depletion on CO2-induced anxiety in patients with panic disorder and normal volunteers

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BACKGROUND: Uncertainties remain about the role of serotonin in the aetiology and treatment of panic disorder.

AIMS: To investigate the effect of reducing brain serotonin function on anxiety at rest, and following 5% CO2 provocation in normal controls and patients with panic disorder.

METHOD: Twenty drug-free patients with DSM-III-R panic disorder and 19 controls received a tryptophan-free amino acid drink on one occasion and a control drink on the other in a double-blind, balanced protocol. 5% CO2 was given as a panic challenge after 270 minutes.

RESULTS: Plasma tryptophan fell by more than 80% both patients and controls after the tryptophan-free drink. Tryptophan depletion did not alter resting anxiety. In patients alone, tryptophan depletion caused a greater anxiogenic response and an increased rate of panic attacks (9 v. 2, P < 0.05) after 5% CO2 challenge. No normal volunteers panicked.

CONCLUSIONS: Serotonin may directly modulate panic anxiety in patients with panic disorder. This may underlie the efficacy of serotonergic antidepressants in treating panic disorder.

Original languageEnglish
Pages (from-to)182-8
Number of pages7
JournalThe British journal of psychiatry : the journal of mental science
Issue number2
Publication statusPublished - Feb 2000


  • Adolescent
  • Adult
  • Aged
  • Analysis of Variance
  • Anxiety
  • Carbon Dioxide
  • Case-Control Studies
  • Female
  • Humans
  • Male
  • Middle Aged
  • Panic Disorder
  • Psychological Tests
  • Serotonin
  • Time Factors
  • Clinical Trial
  • Journal Article
  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't


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