Analysis of 2,638 driver fatalities found that cannabis (THC >2 ng/mL) and amphetamines elevated crash responsibility risk, while prescription opioids, benzodiazepines, and antidepressants alone did not significantly increase crash risk.
Anyone interested in which substances actually increase driving crash risk.
Cannabis elevated crash risk while prescription medications alone did not
What the researchers found
Researchers reviewed coroner files and toxicology records of 2,638 fatally injured drivers in Victoria, Australia over 14 years (2000-2013), representing over 97% of all driver fatalities in the study period.
Drugs were found in 34.4% of fatalities. Each driver was assessed for crash responsibility using a validated method. Cannabis (THC >2 ng/mL in blood) and amphetamines were associated with significantly elevated crash risk compared to drug-free drivers.
In contrast, prescription medications alone (opioids, benzodiazepines, antidepressants including SSRIs) did not show significantly elevated crash risk, though benzodiazepines showed a trend. Sedating antihistamines were detected in 1.1% of fatalities.
Why it matters
This large dataset provides important context for the drugged driving debate. While cannabis and amphetamines elevated crash risk, commonly prescribed medications that many people worry about (opioids, benzodiazepines, antidepressants) did not show statistically significant increases in crash responsibility when used alone.
The numbers in context
2,638 driver fatalities (>97% of all). Drugs found in 34.4%. Alcohol (>=0.05) in 24.8%. Medicinal drugs in 21.2%. Antidepressants: 7.9%. Benzodiazepines: 7.0%. Opioids: 6.6%. Cannabis (THC >2 ng/mL) and amphetamines showed elevated crash risk.
How the study worked
Retrospective analysis of coroner files and toxicology records for all driver fatalities in Victoria, Australia (2000-2013). Crash responsibility was assessed using a validated published method. Drug detection used sensitive analytical limits comparable to those for illicit drugs.
What this study cannot tell us
This analysis cannot determine impairment at the time of the crash, only the presence of drugs in blood. Tolerance effects (regular prescription users may be less impaired than the blood levels suggest) may explain the null finding for prescription drugs. The THC cutoff of 2 ng/mL may not perfectly separate impaired from non-impaired drivers.
How to read the evidence
This is a large retrospective study covering 97% of driver fatalities over 14 years using a validated crash responsibility method, providing strong epidemiological evidence.
When this study was published
Published in 2016, covering 2000-2013 data. Cannabis potency and prescription drug patterns have continued to evolve.
The bigger picture
This study contributes important real-world data distinguishing between substances that actually elevate crash risk and those that are merely detected in fatally injured drivers. The finding that cannabis elevates crash risk while common prescriptions do not informs both clinical prescribing and traffic safety policy.
Questions still open
- Would a higher THC cutoff change the crash risk findings? Do combinations of prescription drugs and cannabis or alcohol show different risk patterns?
Common questions
Is driving on cannabis as dangerous as driving drunk?
Are prescription medications safe to drive on?
Read the original research
The involvement of prescribed drugs in road trauma.
Forensic science international, 265, 17-21
Citation
Drummer, Olaf H; Yap, Suwan. (2016). The involvement of prescribed drugs in road trauma.. Forensic science international, 265, 17-21. https://doi.org/10.1016/j.forsciint.2015.12.050