A systematic review of roadside cannabis screening tests found that existing oral fluid devices can detect recent cannabis use but struggle to reliably indicate actual impairment, creating challenges for enforcement.
Traffic safety researchers, law enforcement, policymakers in legalized jurisdictions, and forensic toxicologists.
Oral fluid devices detect THC but cannot reliably indicate impairment
What the researchers found
Available roadside screening devices, primarily oral fluid-based, can detect THC presence but their ability to identify functional impairment is limited. Sensitivity and specificity varied across devices and cutoff thresholds.
Why it matters
As cannabis legalization expands, effective roadside screening is essential for traffic safety. Unlike alcohol, where breathalyzers directly measure impairment-related blood alcohol levels, cannabis detection does not straightforwardly indicate impairment.
The numbers in context
Multiple roadside screening devices evaluated. Oral fluid testing was the primary modality. Sensitivity and specificity varied by device and THC cutoff threshold.
How the study worked
Systematic review of six databases (inception to March 2020) and grey literature. Included primary studies evaluating test characteristics of roadside cannabis screening compared to laboratory confirmation testing.
What this study cannot tell us
Literature search through March 2020 may miss newer devices. Varied study designs and reference standards across included studies. Roadside conditions differ from laboratory settings. Cannot validate impairment detection, only THC presence detection.
How to read the evidence
Systematic review with appropriate methodology. Limited by heterogeneous study designs and the fundamental challenge of measuring cannabis impairment.
When this study was published
Published 2023. Literature through March 2020.
The bigger picture
The cannabis impairment detection gap is one of the most significant practical challenges of legalization. THC can remain detectable long after impairment has resolved, while some impaired drivers may test below detection thresholds depending on timing.
Questions still open
- Would combining oral fluid THC testing with cognitive/behavioral assessment improve impairment identification? What THC thresholds best balance sensitivity and specificity for enforcement purposes?
Common questions
Can police test for cannabis at the roadside?
Why is testing for cannabis impairment so difficult?
Read the original research
Roadside screening tests for cannabis use: A systematic review.
Heliyon, 9(4), e14630
Citation
Wennberg, Erica; Windle, Sarah B; Filion, Kristian B; Thombs, Brett D; Gore, Genevieve; Benedetti, Andrea; Grad, Roland; Ells, Carolyn; Eisenberg, Mark J. (2023). Roadside screening tests for cannabis use: A systematic review.. Heliyon, 9(4), e14630. https://doi.org/10.1016/j.heliyon.2023.e14630