The effects of dietary neurotransmitter precursors on human behavior

Am J Clin Nutr. 1985 Aug;42(2):366-70. doi: 10.1093/ajcn/42.2.366.


The neurotransmitter precursors tryptophan and tyrosine are present in a variety of foods. In order to document possible effects of tryptophan and tyrosine on human behavior, single oral doses of these substances and matched placebos were administered to 20 men in a double-blind, crossover study. Various tests of mood state and performance were then administered. Tryptophan increased subjective fatigue and decreased self-ratings of vigor and alertness, but did not impair performance on any of the tests. Tyrosine produced no effects in our young population compared with placebo, but did decrease reaction time relative to tryptophan. It may be concluded that tryptophan has significant sedative-like properties, but unlike other sedatives may not impair performance.

Publication types

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

MeSH terms

  • Adult
  • Auditory Perception / drug effects
  • Behavior / drug effects*
  • Diet*
  • Emotions / drug effects
  • Humans
  • Male
  • Middle Aged
  • Psychomotor Performance / drug effects
  • Self-Assessment
  • Tryptophan / pharmacology*
  • Tyrosine / pharmacology*
  • Visual Perception / drug effects


  • Tyrosine
  • Tryptophan