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.

Copyright © 2013 John Wiley & Sons, Ltd.