The effect of tryptophan depletion and enhancement on subjective and behavioural aggression in normal male subjects

Psychopharmacology (Berl). 1995 Mar;118(1):72-81. doi: 10.1007/BF02245252.


In order to investigate the link between aggression and 5-HT, we looked at effects of changes in plasma tryptophan on healthy male subjects. Twenty-four with high trait aggression (H) and 24 with low (L) drank an amino acid mixture with (T+) or without (T-) tryptophan. These caused plasma tryptophan enhancement and depletion, respectively, at 4.5 h. Group H subjects given T- became more angry, aggressive, annoyed, hostile and quarrelsome on subjective measures, whereas those given T+ responded in the opposite way. On a behavioural measure of aggression, group H subjects responded more aggressively after T- than T+. In contrast, there was no consistent effect on subjective or behavioural aggression in group L subjects. Feelings of well-being in group H were decreased by T- and increased by T+. In group L, T+ reduced feelings of well-being, possibly due to the sedative effect of tryptophan in this group, which correlated positively with plasma tryptophan concentration. Changes in plasma tryptophan are probably followed by changes in central 5-HT turnover. We conclude that, in those with pre-existing aggressive traits, acute falls in central 5-HT can cause increased subjective and objective aggression, while rises can have the opposite effect. The absence of changes in a low aggressive group suggests that the primary effect may be on impulsivity, possibly mediated by 5-HT1a receptors, expressing underlying aggressive traits. The findings on mood changes provide support for earlier reports of a lowering of mood with tryptophan depletion.

Publication types

  • Clinical Trial
  • Controlled Clinical Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Affect / drug effects
  • Aggression / drug effects*
  • Amino Acids / blood
  • Amino Acids / pharmacology
  • Anger / drug effects
  • Anxiety / psychology
  • Galvanic Skin Response / drug effects
  • Humans
  • Male
  • Reaction Time / drug effects
  • Tryptophan / blood
  • Tryptophan / physiology*


  • Amino Acids
  • Tryptophan