Effects of Alterations in Plasma Tryptophan Levels on Aggressive Feelings

We read with interest the recent correspondence with regard to the dangers of amino acid supplements, given the effect of tryptophan-free amino acid mixtures in lowering mood.¹ We have been using the technique of rapid enhancement or depletion of plasma tryptophan levels to investigate the control of aggression. Recent work² has suggested that impulsivity rather than aggression, per se, may be affected by central serotonin function. Thus, in depressed patients, reduced serotonin activity is associated with suicide,³ and in violent offenders, with measures of aggression and hostility²; the changes in impulsivity are manifested by the underlying traits. Previous studies that measured provoked aggression⁴ and subjective hostility⁵ after tryptophan depletion have not measured preexisting aggressive traits, which may have accounted for their failure to find an effect.

We looked at 24 male subjects who were selected because they had high levels of trait aggression based a