Cannabis effects on driving skills.

Area of Science:

• Forensic Toxicology
• Traffic Safety Research
• Cannabinoid Pharmacology

Background:

• Cannabis is frequently detected in impaired drivers, complicating legal and legislative efforts.
• Previous research faced challenges due to sample collection delays, metabolite analysis, and polydrug use.

Purpose of the Study:

• To review and evaluate existing literature on cannabis' effects on driving.
• To highlight epidemiologic and experimental data concerning driver impairment after cannabis consumption.

Main Methods:

• Literature review and evaluation of epidemiologic and experimental studies.
• Analysis of data on motor vehicle accident (MVA) risk, driver culpability, and performance on driving-related tasks.
• Comparison of results based on biological matrices (blood vs. urine) and participant smoking frequency.

Main Results:

• Epidemiologic data indicate a 2-fold increase in MVA risk post-cannabis smoking.
• Increased blood THC concentrations correlate with higher driver culpability.
• Experimental studies demonstrate impaired cognitive function, lane weaving, and deterioration in complex task performance, even in frequent smokers.
• Urine-based studies did not consistently show a crash risk association.

Conclusions:

• Inconsistencies in findings are often due to differing study designs and confounding factors.
• Blood THC concentrations of 2-5 ng/mL are linked to significant driving impairment, particularly in occasional users.
• Future research should focus on complex tasks and include both occasional and chronic cannabis smokers.