The effects of tryptophan depletion and loading on laboratory aggression in men: time course and a food-restricted control

Psychopharmacology (Berl). 1999 Feb;142(1):24-30. doi: 10.1007/s002130050858.


Some studies have shown that sharp reduction of L-tryptophan (Trp) concentration in plasma results in increases in laboratory-measured aggression. Conversely, raising plasma Trp has blunted aggression. These effects are presumably due to impaired or enhanced serotonin synthesis and neurotransmission in the brain. In this study, the laboratory-measured aggressive behavior of eight men under both Trp depletion (T-) and Trp loading (T+) conditions was compared to their aggressive behavior under food-restricted control conditions (overnight fast without an amino acid beverage). Subjects were provoked by periodic subtraction of money which was attributed to a fictitious other participant, and aggression was defined as the number of retaliatory responses the subject made ostensibly to reduce the earnings of the (fictitious) other participant. Following ingestion of the T- beverage, aggressive responding was significantly elevated relative to the food-restricted control condition, and this increased aggressive behavior became more pronounced across behavioral testing sessions on a time-course which paralleled previously documented decreases in plasma Trp concentrations. In contrast, no changes were observed in aggressive responding under T+ conditions relative to food-restricted conditions. These within-subject behavioral changes under depleted plasma Trp conditions support earlier indications of a role of serotonin in regulating aggression.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aggression / drug effects*
  • Arousal / drug effects
  • Conditioning, Psychological / drug effects
  • Diet / adverse effects
  • Humans
  • Male
  • Reward
  • Time Factors
  • Tryptophan / blood
  • Tryptophan / deficiency*
  • Tryptophan / metabolism
  • Tryptophan / pharmacology*


  • Tryptophan