Oral administration of 5-hydroxytryptophan (5-HTP) impairs decision making under ambiguity but not under risk: evidence from the Iowa Gambling Task.
OBJECTIVE
Although the serotonin precursor 5-hydroxytryptophan (5-HTP) is marketed as a psychoactive nutritional supplement, knowledge is limited regarding the effects of exogenous 5-HTP on brain activity. This study examined if oral administration of 5-HTP to healthy adults impacted: (1) mood states, as measured by the Profile of Mood States (POMS); and (2) performance on the Iowa Gambling Task (IGT), a measure sensitive to alterations in frontocortical serotonin levels.


METHODS
A sample of 46 undergraduates participated, and each received either two 50 mg 5-HTP capsules or placebos, and completed the IGT and POMS following an absorption period.


RESULTS
5-HTP did not significantly alter mood states, but did impair performance on the IGT. Specifically, the 5-HTP group performed more poorly than the placebo group during the first 20 trials of the IGT but did not differ from the placebo group on trials 21-100. This suggests that oral 5-HTP specifically impaired decision making under ambiguity but not under risk. Males also performed more poorly on the first 20 trials of the IGT, regardless of treatment group.


CONCLUSIONS
Oral 5-HTP is psychoactive at low doses. Decisions made under ambiguity may be differentially sensitive to increased serotonin release or associated reductions in frontocortical dopamine activity.
Gendle
Mathew H
MH
Department of Psychology, Elon University, Elon, North Carolina 27244, USA. mgendle@elon.edu
Golding
Abbe C
AC
D006916:5-Hydroxytryptophan / Q000008:administration & dosage / Q000494:pharmacology*; D000284:Administration, Oral; D000339:Affect / Q000187:drug effects; D003657:Decision Making / Q000187:drug effects*; D019587:Dietary Supplements; D004311:Double-Blind Method; D005260:Female; D005715:Gambling / Q000523:psychology*; D006801:Humans; D007600:Judgment; D008297:Male; D009483:Neuropsychological Tests; D011340:Problem Solving; D011619:Psychotropic Drugs / Q000008:administration & dosage / Q000494:pharmacology*; D012306:Risk; D012737:Sex Factors; D013334:Students; D055815:Young Adult
D011619:Psychotropic Drugs; D006916:5-Hydroxytryptophan