Occasional cannabis smokers showed more psychomotor impairment than frequent smokers after the same dose
After smoking the same cannabis cigarette, occasional users showed significantly more impairment on tracking and divided attention tasks than frequent users, suggesting tolerance to psychomotor effects.
Quick Facts
What This Study Found
Fourteen frequent cannabis smokers (4+ times per week) and 11 occasional smokers (less than twice per week) smoked a single 6.8% THC cigarette in a controlled setting. Performance was tested on tracking, divided attention, working memory, and risk-taking tasks at multiple time points.
Occasional smokers showed significantly more difficulty on the critical tracking task 1.5 hours after smoking. Divided attention was also more impaired in occasional users, with group differences in tracking error, hit rate, false alarms, and reaction time. However, working memory and risk-taking showed no group differences.
The findings suggest that frequent cannabis users develop some tolerance to the psychomotor-impairing effects of THC, which has direct implications for interpreting impairment in driving-under-the-influence cases.
Key Numbers
14 frequent smokers (4+/week) and 11 occasional smokers (<2/week). One 6.8% THC cigarette. Occasional smokers significantly more impaired at 1.5 hours. No group differences on working memory or risk-taking tasks.
How They Did This
Controlled laboratory study where 14 frequent and 11 occasional cannabis smokers entered a secure research unit approximately 19 hours before smoking one 6.8% THC cigarette. Performance was assessed at -1.75, 1.5, 3.5, 5.5, and 22.5 hours post-smoking using critical tracking, divided attention, n-back, and Balloon Analog Risk tasks.
Why This Research Matters
Driving impairment laws often treat all cannabis users the same. This study shows that the same dose produces very different levels of impairment depending on use frequency, which complicates the development of fair impairment thresholds.
The Bigger Picture
Tolerance to cannabis effects is well-documented for subjective "high" but less studied for actual psychomotor performance. This study confirms tolerance extends to skills relevant for driving, which challenges one-size-fits-all impairment testing approaches.
What This Study Doesn't Tell Us
Relatively small sample sizes. Single dose of moderate-potency cannabis. Laboratory tasks may not fully capture real-world driving complexity. 19 hours of abstinence before the session may not reflect typical use patterns for frequent users.
Questions This Raises
- ?Should impairment testing account for use frequency?
- ?At what level of tolerance does psychomotor impairment become negligible?
- ?Do frequent users still show impairment at higher doses?
Trust & Context
- Key Stat:
- Occasional smokers significantly more impaired on tracking and attention
- Evidence Grade:
- Controlled laboratory study with standardized dosing and multiple time-point assessments, though sample sizes were modest.
- Study Age:
- Published in 2015. Cannabis potency has increased since this study used 6.8% THC.
- Original Title:
- Smoked cannabis' psychomotor and neurocognitive effects in occasional and frequent smokers.
- Published In:
- Journal of analytical toxicology, 39(4), 251-61 (2015)
- Authors:
- Desrosiers, Nathalie A(3), Ramaekers, Johannes G(12), Chauchard, Emeline(3), Gorelick, David A, Huestis, Marilyn A
- Database ID:
- RTHC-00946
Evidence Hierarchy
Participants are randomly assigned to treatment or placebo groups to test cause and effect.
What do these levels mean? →Frequently Asked Questions
Does frequent cannabis use reduce impairment?
In this study, frequent users showed less psychomotor impairment after the same dose compared to occasional users, suggesting partial tolerance to performance-related effects. This does not mean frequent users are unimpaired.
Which skills were most affected?
Tracking ability and divided attention were the most impaired, particularly in occasional users. Working memory and risk-taking behavior were not significantly different between groups.
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Cite This Study
https://rethinkthc.com/research/RTHC-00946APA
Desrosiers, Nathalie A; Ramaekers, Johannes G; Chauchard, Emeline; Gorelick, David A; Huestis, Marilyn A. (2015). Smoked cannabis' psychomotor and neurocognitive effects in occasional and frequent smokers.. Journal of analytical toxicology, 39(4), 251-61. https://doi.org/10.1093/jat/bkv012
MLA
Desrosiers, Nathalie A, et al. "Smoked cannabis' psychomotor and neurocognitive effects in occasional and frequent smokers.." Journal of analytical toxicology, 2015. https://doi.org/10.1093/jat/bkv012
RethinkTHC
RethinkTHC Research Database. "Smoked cannabis' psychomotor and neurocognitive effects in o..." RTHC-00946. Retrieved from https://rethinkthc.com/research/desrosiers-2015-smoked-cannabis-psychomotor-and
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.