Both per se blood concentration limits and standard field sobriety tests have fundamental limitations for detecting cannabis-impaired driving, with poor correlation between THC levels and actual impairment and no validated functional test for cannabis.
Cannabis users who drive, law enforcement, policymakers, and anyone interested in the science of impaired driving detection.
Cannabis doubles crash risk, but no reliable detection method exists for cannabis impairment
What the researchers found
Unlike alcohol, THC blood concentrations poorly correspond to amount consumed, crash risk, or degree of impairment. Standard field sobriety tests have not been developed or validated for cannabis, and cannabis impairment is difficult to distinguish from effects of aging or certain medications.
Why it matters
Cannabis use doubles automobile crash risk, yet neither of the two standard approaches for detecting impaired driving works reliably for cannabis. This leaves both cannabis users and law enforcement without clear guidance on driving fitness after use.
The numbers in context
Cannabis associated with approximately 2-fold increase in crash risk. Per se THC limits poorly predict impairment. No validated field sobriety test for cannabis. Cannabis impairment difficult to distinguish from aging or medication effects.
How the study worked
Perspective review examining the strengths and limitations of two cannabis-impaired driving detection approaches: per se blood/breath concentration tests and functional field sobriety tests, compared against their established use for alcohol detection.
What this study cannot tell us
Perspective piece rather than systematic review. The 2-fold crash risk estimate varies across studies. Individual tolerance differences make any per se limit inherently imprecise. Technology may improve faster than this review anticipated.
How to read the evidence
Moderate: well-argued perspective synthesizing existing evidence, though not a systematic review.
When this study was published
Published in 2019.
The bigger picture
The author argues that instead of trying to develop substance-specific detection methods for every possible intoxicant, general impairment detection strategies that work regardless of cause would be more practical and equitable.
Questions still open
- Could technology-based impairment assessments (reaction time apps, eye tracking) provide substance-agnostic detection? At what point after use is it actually safe to drive? Should legal frameworks shift from substance detection to impairment detection?
Common questions
Why can't police test for cannabis impairment like they do for alcohol?
What's the solution for cannabis-impaired driving detection?
Read the original research
Strengths and limitations of two cannabis-impaired driving detection methods: a review of the literature.
The American journal of drug and alcohol abuse, 45(6), 610-622
Citation
Ginsburg, Brett C. (2019). Strengths and limitations of two cannabis-impaired driving detection methods: a review of the literature.. The American journal of drug and alcohol abuse, 45(6), 610-622. https://doi.org/10.1080/00952990.2019.1655568
Explore the wider topic
- Surviving 4/20 Sober: A Practical Survival Guide
- CBT for Cannabis Recovery: How Cognitive Behavioral Therapy Works
- The Cannabis Relapse Cycle: Quit, Feel Good, Get Complacent, Repeat
- Cold Turkey vs Tapering: Which Way to Quit Weed
- Dating Sober After Years of Being High: What Nobody Tells You
- Exercise as Medicine: Working Out After Quitting Weed
- Grieving Weed Itself: Mourning the Loss of a Companion
- How to Help Someone Quit Weed (When They're Not Ready)
- How to Quit Weed: A No-Judgment Step by Step Guide
- Journaling Through Weed Withdrawal: Why Writing Helps You Heal
- MA vs SMART Recovery vs Therapy: Comparing Your Options
- Meditation and Mindfulness for Weed Withdrawal
- Your Partner Still Smokes Weed: How to Navigate It
- Quitting Weed While Your Partner Still Smokes
- The Pink Cloud Effect: When Quitting Weed Feels Too Good
- How to Quit Smoking Weed Cold Turkey: What to Expect
- Quit Weed or Cut Back: Which Is Right for You?
- I Quit Weed and Regret It: An Honest Look at Non-Linear Recovery
- Quitting Weed in Your 20s: Career, Social Life, Starting Over
- Quitting Weed in Your 30s: It's Not Too Late
- Quitting Weed After 10+ Years of Daily Use: What to Expect
- Quitting Weed During a Life Crisis: Divorce, Job Loss, and Other Bad Timing
- Quitting Weed and Working Out: How Exercise Helps Recovery
- Quitting Weed After Loss: When Grief Comes Flooding Back
- Quitting Weed When It's Legal Everywhere
- Weed Withdrawal Success Stories: Real People Who Made It Through
- Quitting Weed Long Distance: When You Can't Remove Triggers
- I Relapsed on Weed. Now What? A Practical Reset Guide
- I Relapsed After Quitting Weed: What Now?
- Should I Quit Weed? A Decision Framework (Not a Lecture)
- Quitting Weed at Music Festivals and Concerts: A Sober Survival Guide
- Supplements That Actually Help with Weed Withdrawal (And Ones That Don't)
- How to Tell Your Friends You're Quitting Weed
- Relapse Prevention Plan for Cannabis: A CBT-Based Approach
- Why Weed Relapse Happens: The Science Behind Going Back
- Replacing the Ritual: What to Do When You Quit Weed
- How Cannabis Damaged My Relationships: Before and After
- Social Media Detox from Weed Content