THC impaired performance on standard computer-based cognitive tasks but most phone-based equivalents failed to detect the impairment, raising doubts about the feasibility of a phone app as a cannabis field sobriety test.
People interested in cannabis impairment testing, DUI policy, and workplace safety.
Most phone tasks failed to detect THC impairment
What the researchers found
Across two double-blind studies with oral THC (7.5 and 15 mg), standard computer tasks detected impairment in cognitive speed, reaction time, and working memory. However, most brief phone-based versions of the same tasks did not detect THC-induced impairment.
Why it matters
Unlike alcohol breathalyzers, there is no reliable quick test for cannabis impairment. This study shows how difficult it is to compress cognitive testing into a brief, phone-friendly format sensitive enough to detect THC effects.
The numbers in context
Two studies, n=24 each. THC doses: 7.5 mg and 15 mg oral. Computer tasks detected impairment; most phone tasks did not.
How the study worked
Two double-blind, within-subjects studies (n=24 each) with healthy non-daily cannabis users. Participants received oral THC capsules (0, 7.5, 15 mg) in three sessions. At peak drug effect, they completed both standard computer-based cognitive tasks and brief phone-based tasks measuring speed, reaction time, fine motor ability, working memory, and time perception.
What this study cannot tell us
Small sample sizes (24 per study). Only oral THC was tested; smoked or vaped cannabis may produce different impairment patterns. The phone tasks were prototypes, not a fully developed app.
How to read the evidence
Moderate: two randomized, double-blind, placebo-controlled studies, but small sample sizes and prototype measures.
When this study was published
Published in 2019.
The bigger picture
Law enforcement and employers want a practical way to test for cannabis impairment, similar to alcohol breathalyzers. This research suggests that simple phone-based apps may be too brief and insensitive to fill that role.
Questions still open
- Could longer or more complex phone tasks achieve sufficient sensitivity? Would combining multiple brief measures into a composite score improve detection? How does oral THC impairment compare to inhaled THC impairment on these measures?
Common questions
Why is building a cannabis impairment test so hard?
Could a phone app ever work for this?
Read the original research
Developing a phone-based measure of impairment after acute oral ∆9-tetrahydrocannabinol.
Journal of psychopharmacology (Oxford, England), 33(9), 1160-1169
Citation
Pabon, Elisa; de Wit, Harriet. (2019). Developing a phone-based measure of impairment after acute oral ∆9-tetrahydrocannabinol.. Journal of psychopharmacology (Oxford, England), 33(9), 1160-1169. https://doi.org/10.1177/0269881119862533