Effects of oral 5-hydroxytryptophan on a standardized planning task: insight into possible dopamine/serotonin interactions in the forebrain

Hum Psychopharmacol. 2013 May;28(3):270-3. doi: 10.1002/hup.2314. Epub 2013 Apr 22.


Objective: Several studies have suggested that exogenous administration of the serotonin precursor 5-hydroxytryptophan (5-HTP) can result in the ectopic production of serotonin in dopaminergic neurons and a concomitant reduction in dopamine release. This study tested this hypothesis using the Tower of London (TOL), a test of planning and executive control that is sensitive to changes in forebrain dopamine activity, but insensitive to alterations in serotonin.

Methods: A sample of 68 undergraduates participated, and each received either three 50-mg 5-HTP capsules or placebos, and completed the TOL following a set absorption period.

Results: 5-HTP significantly lengthened the average time needed to complete each of the 10 trials of the TOL. 5-HTP did not affect accuracy on this task.

Conclusions: Oral exogenous 5-HTP disrupts dopaminergic function in the human forebrain.

Publication types

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

MeSH terms

  • 5-Hydroxytryptophan / administration & dosage
  • 5-Hydroxytryptophan / pharmacology*
  • Administration, Oral
  • Adolescent
  • Antidepressive Agents, Second-Generation / administration & dosage
  • Antidepressive Agents, Second-Generation / pharmacology*
  • Dopamine / metabolism*
  • Double-Blind Method
  • Executive Function / drug effects
  • Female
  • Humans
  • Male
  • Neuropsychological Tests
  • Prosencephalon / drug effects
  • Prosencephalon / metabolism
  • Serotonin / metabolism*
  • Time Factors
  • Young Adult


  • Antidepressive Agents, Second-Generation
  • Serotonin
  • 5-Hydroxytryptophan
  • Dopamine