Objective pupillometer measurements showed diminished pupil dynamics (how pupils respond to light) were more predictive of recent cannabis use than pupil size alone, with moderate accuracy at 40 and 100 minutes post-use.
Traffic safety researchers, forensic toxicologists, law enforcement, drug testing researchers
Pupil dynamics predicted recent cannabis use with moderate accuracy (AUC 0.73-0.75)
What the researchers found
The most predictive pupillary measure was percent change in pupil size, which decreased after cannabis use, with an area under the curve of 0.73 at 40 minutes and 0.75 at 100 minutes. Pupil size alone (measured in darkness) did not reliably change after cannabis use. Diminished pupil dynamics (constriction to light and recovery dilation) were more predictive than static pupil size.
Why it matters
Law enforcement currently relies on subjective assessment of eye changes during drug recognition evaluations. This study tested whether objective pupillometer measurements could improve detection accuracy, finding moderate but imperfect predictive value.
The numbers in context
126 participants; AUC 0.73 at 40 min and 0.75 at 100 min for percent change in pupil size; maximum pupil size in darkness not reliably changed; diminished constriction and recovery dilation more predictive; combining multiple measures did not meaningfully improve prediction
How the study worked
126 participants assessed with a NeurOptics PLR-3000 pupillometer at baseline and at 40 and 100 minutes after ad libitum cannabis inhalation (95 cannabis users, 31 controls). Sensitivity, specificity, and accuracy calculated for multiple pupillary measures.
What this study cannot tell us
Moderate predictive accuracy (AUC 0.73-0.75) means significant false positive and negative rates, participants used their own cannabis products creating dosing variability, pupil dynamics can be affected by other substances and medical conditions, laboratory conditions differ from roadside testing
How to read the evidence
Well-designed controlled study with objective measurements; moderate accuracy limits practical standalone application
When this study was published
Published 2025
The bigger picture
The search for reliable, objective markers of recent cannabis use continues to challenge both researchers and policymakers. Pupillary dynamics show promise but cannot yet serve as a standalone test, suggesting they might work best as part of a multi-measure assessment.
Questions still open
- Could pupillometry combined with other objective measures (balance, cognitive tests) improve detection accuracy? How do different cannabis products affect pupillary dynamics? Would the test perform differently in naive vs. tolerant users?
Common questions
Can a pupil test tell if someone recently used cannabis?
Why not just measure pupil size?
Read the original research
Pupillary dynamics as a marker of acute cannabis inhalation.
Clinical toxicology (Philadelphia, Pa.), 63(11), 869-877
Citation
Brooks-Russell, Ashley; Godbole, Suneeta; Kosnett, Michael J; Limbacher, Sarah; Subramanian, Prem S; Brown, Timothy; Wrobel, Julia. (2025). Pupillary dynamics as a marker of acute cannabis inhalation.. Clinical toxicology (Philadelphia, Pa.), 63(11), 869-877. https://doi.org/10.1080/15563650.2025.2543066