, Volume 118, Issue 1, pp 72–81 | Cite as

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

  • A. J. Cleare
  • A. J. Bond
Original Investigation


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−) trytophan. 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 trytophan 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.

Key words

Tryptophan depletion Tryptophan Aggression Mood Serotonin 5-HT1a receptor Impulsivity 


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Copyright information

© Springer-Verlag 1995

Authors and Affiliations

  • A. J. Cleare
    • 1
  • A. J. Bond
    • 1
  1. 1.Institute of PsychiatryLondonUKI

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