Pupil Response Changes Could Help Detect Recent Cannabis Use
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.
Quick Facts
What This Study 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.
Key Numbers
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 They Did This
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.
Why This Research 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 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.
What This Study Doesn't 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
Questions This Raises
- ?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?
Trust & Context
- Key Stat:
- Pupil dynamics predicted recent cannabis use with moderate accuracy (AUC 0.73-0.75)
- Evidence Grade:
- Well-designed controlled study with objective measurements; moderate accuracy limits practical standalone application
- Study Age:
- Published 2025
- Original Title:
- Pupillary dynamics as a marker of acute cannabis inhalation.
- Published In:
- Clinical toxicology (Philadelphia, Pa.), 63(11), 869-877 (2025)
- Authors:
- Brooks-Russell, Ashley(20), Godbole, Suneeta(2), Kosnett, Michael J(6), Limbacher, Sarah, Subramanian, Prem S, Brown, Timothy, Wrobel, Julia
- Database ID:
- RTHC-06121
Evidence Hierarchy
Watches what happens naturally without intervening.
What do these levels mean? →Frequently Asked Questions
Can a pupil test tell if someone recently used cannabis?
With moderate accuracy. Changes in how the pupil responds to light (not its resting size) were the best predictor, correctly identifying recent cannabis use about 73-75% of the time.
Why not just measure pupil size?
Cannabis did not reliably change maximum pupil size in darkness. Instead, it was the dynamic response (how pupils constrict and recover after light exposure) that was altered, likely reflecting cannabis effects on autonomic nervous system function.
Read More on RethinkTHC
Cite This Study
https://rethinkthc.com/research/RTHC-06121APA
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
MLA
Brooks-Russell, Ashley, et al. "Pupillary dynamics as a marker of acute cannabis inhalation.." Clinical toxicology (Philadelphia, 2025. https://doi.org/10.1080/15563650.2025.2543066
RethinkTHC
RethinkTHC Research Database. "Pupillary dynamics as a marker of acute cannabis inhalation." RTHC-06121. Retrieved from https://rethinkthc.com/research/brooks-russell-2025-pupillary-dynamics-as-a
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.