Field Sobriety Tests Failed to Detect Cannabis Impairment
In a controlled study of 20 adults, standard field sobriety tests showed little sensitivity to cannabis impairment, while a novel app-based test (DRUID) reliably detected impairment from both oral and vaporized cannabis.
Quick Facts
What This Study Found
High-dose oral and vaporized cannabis impaired cognitive and psychomotor performance, but field sobriety tests showed little sensitivity to cannabis-induced impairment. The DRUID app was the most sensitive test, detecting significant differences from placebo for both administration routes. Blood THC levels returned to baseline before impairment resolved.
Key Numbers
20 participants (10 men, 10 women); 6 sessions; low doses produced subjective effects but no measurable impairment; high doses impaired performance; DRUID detected impairment at both routes; women showed more DRUID impairment at high vaporized dose; blood THC returned to baseline before impairment resolved.
How They Did This
Double-blind, placebo-controlled, six-session outpatient study with 20 infrequent cannabis users (10 men, 10 women) receiving three oral doses (0, 10, 25 mg THC brownies) and three vaporized doses (0, 5, 20 mg THC), tested with computerized tasks, DRUID app, and field sobriety tests.
Why This Research Matters
Current roadside methods for detecting cannabis impairment are inadequate. Blood THC levels and field sobriety tests both fail to reliably identify when someone is actually impaired, creating significant public safety and legal challenges.
The Bigger Picture
The disconnect between blood THC concentrations and actual impairment undermines per se legal limits for THC, while the failure of field sobriety tests suggests entirely new approaches are needed for roadside cannabis impairment detection.
What This Study Doesn't Tell Us
Small sample size (20 participants); infrequent users only (tolerance effects not captured); lab setting differs from real-world driving; limited dose range; DRUID validation still early.
Questions This Raises
- ?Could the DRUID app or similar tools replace field sobriety tests for cannabis at roadside?
- ?Should per se THC blood limits be abandoned in favor of impairment-based assessments?
Trust & Context
- Key Stat:
- Blood THC levels returned to baseline before cannabis impairment actually subsided
- Evidence Grade:
- Small but well-designed double-blind RCT with placebo control, limited by sample size and lab setting.
- Study Age:
- Published in 2021.
- Original Title:
- Assessment of cognitive and psychomotor impairment, subjective effects, and blood THC concentrations following acute administration of oral and vaporized cannabis.
- Published In:
- Journal of psychopharmacology (Oxford, England), 35(7), 786-803 (2021)
- Authors:
- Spindle, Tory R(18), Martin, Erin L(7), Grabenauer, Megan(2), Woodward, Thomas, Milburn, Michael A, Vandrey, Ryan
- Database ID:
- RTHC-03544
Evidence Hierarchy
Participants are randomly assigned to treatment or placebo groups to test cause and effect.
What do these levels mean? →Frequently Asked Questions
Can police tell if someone is high while driving?
This study found that standard field sobriety tests showed little sensitivity to cannabis impairment. A novel app-based test (DRUID) performed significantly better, suggesting new tools are needed for roadside testing.
Does blood THC level indicate impairment?
No. In this study, blood THC concentrations returned to baseline well before actual impairment resolved, meaning someone could test "clean" on blood THC while still being impaired by cannabis.
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Cite This Study
https://rethinkthc.com/research/RTHC-03544APA
Spindle, Tory R; Martin, Erin L; Grabenauer, Megan; Woodward, Thomas; Milburn, Michael A; Vandrey, Ryan. (2021). Assessment of cognitive and psychomotor impairment, subjective effects, and blood THC concentrations following acute administration of oral and vaporized cannabis.. Journal of psychopharmacology (Oxford, England), 35(7), 786-803. https://doi.org/10.1177/02698811211021583
MLA
Spindle, Tory R, et al. "Assessment of cognitive and psychomotor impairment, subjective effects, and blood THC concentrations following acute administration of oral and vaporized cannabis.." Journal of psychopharmacology (Oxford, 2021. https://doi.org/10.1177/02698811211021583
RethinkTHC
RethinkTHC Research Database. "Assessment of cognitive and psychomotor impairment, subjecti..." RTHC-03544. Retrieved from https://rethinkthc.com/research/spindle-2021-assessment-of-cognitive-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.