Effects of tryptophan depletion on anxiety and on panic provoked by carbon dioxide challenge

Psychiatry Res. 1998 Feb 27;77(3):167-74. doi: 10.1016/s0165-1781(98)00004-3.


Results of several studies suggest that anxiety is under serotonergic control. We studied the influence of tryptophan depletion on generalized anxiety and on the response to a 35% carbon dioxide (CO2) challenge. Fifteen healthy male volunteers received both a mixture of amino acids without tryptophan and a placebo mixture under double-blind conditions. The tryptophan-free mixture led to an 80% decrease in blood tryptophan levels compared to the placebo. There was a significant increase in anxiety on the Spielberger Anxiety Inventory and a trend towards more tension on the Profile of Mood States-'tension' items, both of which were interpreted as increased nervousness. Furthermore, a significant increase in neurovegetative panic symptoms occurred after the CO2 challenge. We conclude that the serotonergic system is causally involved in anxiety-related mechanisms and that it may be worth pursuing the role of tryptophan depletion on CO2-induced panic in patients with anxiety disorders.

Publication types

  • Clinical Trial
  • Randomized Controlled Trial

MeSH terms

  • Adult
  • Anxiety / diagnosis
  • Anxiety / physiopathology*
  • Arousal / physiology
  • Carbon Dioxide*
  • Cross-Over Studies
  • Double-Blind Method
  • Humans
  • Male
  • Panic / physiology*
  • Personality Inventory
  • Serotonin / physiology*
  • Tryptophan / deficiency*


  • Carbon Dioxide
  • Serotonin
  • Tryptophan