Occasional Stimulant Users With High Cannabis Use Showed the Most Brain Inefficiency During Decision-Making
Occasional stimulant users showed inefficient brain activation during learned decision-making, and this effect was driven primarily by those with high cannabis co-use, suggesting additive effects of cocaine and cannabis on reward circuits.
Quick Facts
What This Study Found
One hundred sixty-one occasional stimulant users and 48 controls performed a decision-making task during fMRI. Stimulant users showed greater anterior insula, inferior frontal gyrus, and dorsal striatum activation during late trials (when contingencies were already learned), suggesting they needed more brain resources to execute familiar decisions.
Follow-up analyses revealed that this inefficiency was driven by the subgroup with high cannabis co-use. Occasional stimulant users with high cannabis use showed significantly greater activation than controls, while those with low cannabis use did not differ from controls. Cocaine users also showed greater inefficiency than prescription stimulant users.
Key Numbers
161 stimulant users, 48 controls. Greater activation in anterior insula, IFG, dorsal striatum during late trials. High cannabis subgroup: significantly greater activation than controls. Low cannabis subgroup: no difference from controls. Cocaine users > prescription stimulant users.
How They Did This
Cross-sectional fMRI study. 161 occasional stimulant users and 48 controls. Paper-Scissors-Rock task with changing win probabilities. BOLD fMRI during early (learning) and late (execution) trials. Subgroup analyses by cannabis use level and stimulant preference.
Why This Research Matters
This study suggests that cannabis and cocaine have additive negative effects on brain efficiency during decision-making. The inefficiency appeared during execution of already-learned contingencies, not during learning itself, suggesting the drugs affect the deployment of learned strategies rather than learning capacity.
The Bigger Picture
The finding that cannabis co-use amplifies stimulant-related brain inefficiency has implications for understanding polysubstance use. Rather than one drug dominating the cognitive effects, the combination appears to produce additive or synergistic impairment in reward-based decision circuits.
What This Study Doesn't Tell Us
Cross-sectional design cannot determine causation or temporal ordering. "Occasional" stimulant use is a heterogeneous category. Cannabis use was a post-hoc subgroup variable. The task measures a specific type of decision-making. Greater brain activation does not always mean inefficiency; it could reflect compensatory effort.
Questions This Raises
- ?Does this brain inefficiency predict progression to stimulant dependence?
- ?Would reducing cannabis use improve decision-making efficiency in stimulant users?
- ?Are the effects reversible with abstinence?
- ?Could the inefficiency be a pre-existing vulnerability?
Trust & Context
- Key Stat:
- Brain inefficiency was driven by the high cannabis co-use subgroup
- Evidence Grade:
- Large fMRI study with informative subgroup analyses; moderate evidence for additive cannabis-stimulant effects on brain function.
- Study Age:
- Published in 2013. Polysubstance effects on brain function continue to be an active research area.
- Original Title:
- Young adults at risk for stimulant dependence show reward dysfunction during reinforcement-based decision making.
- Published In:
- Biological psychiatry, 73(3), 235-41 (2013)
- Authors:
- Stewart, Jennifer L(2), Flagan, Taru M, May, April C, Reske, Martina, Simmons, Alan N, Paulus, Martin P
- Database ID:
- RTHC-00738
Evidence Hierarchy
A snapshot of a population at one point in time.
What do these levels mean? →Frequently Asked Questions
Does using cannabis with stimulants make brain effects worse?
This study suggests yes. Occasional stimulant users who also used cannabis heavily showed the most brain inefficiency during decision-making. Those with low cannabis use looked similar to non-drug-using controls. This suggests cannabis and stimulants have additive negative effects on the brain circuits involved in executing learned reward-based decisions.
What does "brain inefficiency" mean?
In this study, occasional stimulant users (especially those with high cannabis co-use) showed greater brain activation than controls to accomplish the same task performance. This means their brains needed to work harder to achieve the same result, like a car engine revving higher to maintain the same speed. This inefficiency appeared specifically when applying already-learned decision rules, not during the learning phase.
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Cite This Study
https://rethinkthc.com/research/RTHC-00738APA
Stewart, Jennifer L; Flagan, Taru M; May, April C; Reske, Martina; Simmons, Alan N; Paulus, Martin P. (2013). Young adults at risk for stimulant dependence show reward dysfunction during reinforcement-based decision making.. Biological psychiatry, 73(3), 235-41. https://doi.org/10.1016/j.biopsych.2012.08.018
MLA
Stewart, Jennifer L, et al. "Young adults at risk for stimulant dependence show reward dysfunction during reinforcement-based decision making.." Biological psychiatry, 2013. https://doi.org/10.1016/j.biopsych.2012.08.018
RethinkTHC
RethinkTHC Research Database. "Young adults at risk for stimulant dependence show reward dy..." RTHC-00738. Retrieved from https://rethinkthc.com/research/stewart-2013-young-adults-at-risk
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.