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

Jane Metrik, Christopher W. Kahler, Brady Reynolds, John E. Mc Geary, Peter M. Monti, Margaret Haney, Harriet De Wit, Damaris J. Rohsenow

Research output: Contribution to journalArticlepeer-review

99 Scopus citations


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 regularmarijuana users (N0136)were randomly assigned into one of four groups in a two × two instructional set (Told THC vs. Told no THC) by drug administration (smoked marijuanawith 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.

Original languageEnglish
Pages (from-to)489-499
Number of pages11
Issue number4
StatePublished - Oct 2012

Bibliographical note

Funding Information:
Acknowledgments This study was supported by a grant R01 DA021403 from the National Institute on Drug Abuse to Jane Metrik, a Research Career Development Award from the Medical Research Service of the Department of Veteran Affairs to John McGeary, and Senior Research Career Scientist awards from the Department of Veteran Affairs to Drs. Monti and Rohsenow. The authors gratefully acknowledge Dr. James Harper, III, Amy Mochel, Suzanne Sales, Timothy Souza, and Adrienne Umali for their contribution to the project.


  • Cannabis
  • Expectancy
  • Impulsivity
  • Inhibition
  • Risk taking
  • Sexual risk
  • THC

ASJC Scopus subject areas

  • Pharmacology


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