The effects of alcohol on laboratory-measured impulsivity after L: -Tryptophan depletion or loading

Psychopharmacology (Berl). 2007 Jul;193(1):137-50. doi: 10.1007/s00213-007-0763-6. Epub 2007 Mar 22.


Rationale: Indirect evidence supports a link between serotonergic activity and individual differences in the behavioral response to alcohol, but few studies have experimentally demonstrated that an individual's biological state can influence the sensitivity to alcohol-induced behaviors.

Objective: Our purpose was to temporarily modify serotonin synthesis in healthy individuals to determine how altered biological states may interact with alcohol administration to affect impulsive behavior.

Materials and methods: In a repeated-measures design, 18 normal controls consumed a 50-g L: -tryptophan (Trp) depleting (ATD) or loading (ATL) amino-acid beverage that temporarily decreased or increased (respectively) serotonin synthesis before receiving either a moderate dose of alcohol (0.65 g/kg) or placebo. All participants completed three impulsivity testing sessions on each of the five experimental days. Session one was a baseline session. Session two included testing after ATD-only or ATL-only. Session three included: (1) placebo after ATL (ATL+PBO); (2) placebo after ATD (ATD+PBO); (3) alcohol after ATL (ATL+ALC); (4) alcohol after ATD (ATD+ALC); and (5) Alcohol-only conditions. Impulsivity was assessed using the Immediate Memory Task (Dougherty et al., Behav Res Methods Instrum Comput 34:391-398, 2002), a continuous performance test yielding commission errors that have been previously validated as a component of impulsive behavior.

Results: Primary findings were that ATD-only increased impulsive responding compared to ATL-only, and ATD+ALC increased commission errors to levels higher than either the ATL+ALC or Alcohol-only conditions.

Conclusions: These findings demonstrate that reduced serotonin synthesis can produce increased impulsivity even among non-impulsive normal controls, and that the behavioral effects of alcohol are, in part, dependent on this biological state.

MeSH terms

  • Adult
  • Breath Tests
  • Double-Blind Method
  • Ethanol / adverse effects*
  • Female
  • Humans
  • Impulsive Behavior* / chemically induced
  • Impulsive Behavior* / metabolism
  • Impulsive Behavior* / psychology
  • Male
  • Neuropsychological Tests
  • Serotonin / biosynthesis*
  • Tryptophan* / administration & dosage
  • Tryptophan* / deficiency
  • Tryptophan* / pharmacology


  • Serotonin
  • Ethanol
  • Tryptophan