Of four oral fluid THC testing devices used in nearly 9,000 roadside tests, only one consistently detected THC with high accuracy, while two had sensitivity below 13%.
Policymakers, law enforcement agencies, and anyone interested in cannabis-impaired driving enforcement
Sensitivity ranged from less than 13% to 96.8% across devices
What the researchers found
The Drager DrugTest had 96.8% sensitivity and 97.1% specificity for detecting THC at a 5 ng/mL threshold. In contrast, the AquilaScan and Druglizer devices had sensitivity below 13%, meaning they missed the vast majority of positive samples.
Why it matters
As cannabis-impaired driving enforcement grows, police departments are adopting oral fluid testing devices. This study reveals that device choice matters enormously, with some devices essentially useless for detecting THC.
The numbers in context
Drager DrugTest: 96.8% sensitivity, 97.1% specificity, 97.0% efficiency. WipeAlyser Reader: 91.4% sensitivity, 97.2% specificity. AquilaScan and Druglizer: less than 13% sensitivity. Of 8,945 tests, 530 (5.9%) screened positive for THC.
How the study worked
Researchers conducted 8,945 oral fluid THC screening tests at the roadside using four different devices. Samples that screened positive (530 total, 5.9%) were confirmed by liquid chromatography-tandem mass spectrometry at multiple cutoff concentrations.
What this study cannot tell us
Field conditions (temperature, humidity) may have affected device performance. The study was conducted in one country (Brazil), and device performance may differ in other settings. Only THC was evaluated.
How to read the evidence
Large real-world sample with gold-standard LC-MS/MS confirmation, though conducted at a single location.
When this study was published
2024 study
The bigger picture
Reliable roadside testing is essential for fair enforcement of impaired driving laws. When devices miss most positive cases, impaired drivers go undetected. When they produce false positives, sober drivers face unwarranted consequences.
Questions still open
- Why do some devices perform so poorly in real-world conditions despite presumably passing laboratory testing? Should there be minimum performance standards for roadside oral fluid testing devices?
Common questions
Which roadside THC saliva test performed best?
How reliable are roadside THC tests in general?
Read the original research
Reliability of roadside oral fluid testing devices for ∆9-tetrahydrocannabinol (∆9-THC) detection.
Drug testing and analysis, 16(12), 1528-1536
Citation
Scherer, Juliana Nichterwitz; Vasconcelos, Mailton; Dalanhol, Carolina Silveira; Govoni, Bruna; Dos Santos, Bruno Pereira; Borges, Gabriela Ramos; de Gouveia, Giovanna Cristiano; Viola, Patrícia Pacheco; Carlson, Renato Luiz Romera; Martins, Aline Franco; Costa, Jose Luiz; Huestis, Marilyn A; Pechansky, Flavio. (2024). Reliability of roadside oral fluid testing devices for ∆9-tetrahydrocannabinol (∆9-THC) detection.. Drug testing and analysis, 16(12), 1528-1536. https://doi.org/10.1002/dta.3669