Get access

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


Correspondence to: M. H. Gendle, Department of Psychology, Elon University, 2337 CB, Elon, North Carolina, 27244-2010, USA. Tel: 1-336-278-6431. E-mail:



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.


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.


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.


Oral exogenous 5-HTP disrupts dopaminergic function in the human forebrain. Copyright © 2013 John Wiley & Sons, Ltd.