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Psychopharmacology (Berl). 2012 Oct;223(4):489-99. Epub 2012 May 16.

Balanced placebo design with marijuana: pharmacological and expectancy effects on impulsivity and risk taking.

Author information

  • 1Center for Alcohol and Addiction Studies, Brown University, Box G-S121, Providence, RI 02912, USA. Jane_Metrik@brown.edu

Abstract

RATIONALE:

Marijuana is believed to increase impulsivity and risk taking, but the processes whereby it affects such behaviors are not understood. Indeed, either the pharmacologic effect of delta-9-tetrahydrocannabinol (THC) or the expectancy of receiving it may lead to deficits in cognitive processing and increases in risk taking.

OBJECTIVES AND METHODS:

We examined the relative effects of expecting to receive active marijuana and the pharmacological drug effects using a balanced placebo design. Young adult regular marijuana users (Nā€‰=ā€‰136) were randomly assigned into one of four groups in a two Ɨ two instructional set (Told THC vs. Told no THC) by drug administration (smoked marijuana with 2.8 % THC vs. placebo) design. Dependent measures included subjective intoxication, behavioral impulsivity, and decision-making related to risky behaviors.

RESULTS:

Active THC, regardless of expectancy, impaired inhibition on the Stop Signal and Stroop Color-Word tasks. Expectancy of having smoked THC, regardless of active drug, decreased impulsive decision-making on a delay discounting task among participants reporting no deception and increased perception of sexual risk among women, consistent with a compensatory effect. Expectancy of smoking THC in combination with active THC increased negative perceptions from risky alcohol use. Active drug and expectancy independently increased subjective intoxication.

CONCLUSIONS:

Results highlight the importance of marijuana expectancy effects as users believing they are smoking marijuana may compensate for expected intoxication effects when engaged in deliberate decision-making by making less impulsive and risky decisions. Effects of marijuana on impulsive disinhibition, by contrast, reflect direct pharmacologic effects for which participants did not compensate.

PMID:
22588253
[PubMed - indexed for MEDLINE]
PMCID:
PMC3829473
Free PMC Article
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