Cannabis and Driving: No Impairment After Abstinence

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September 25 2025

Study Overview

New study finds no driving impairment from cannabis after 48 hours of abstinence.Published in Psychopharmacology, September 2025.Examines residual effects on simulated driving performance.

Cannabis Users Study

191 cannabis users participated.Completed 25-minute driving simulator after 48+ hours abstinence.Measured by Composite Drive Score (CDS).No link found between CDS, cannabis history, demographics, or blood THC levels.

Frequent Users vs. Non-Users

Pilot study compared:

• 18 heavy cannabis users (daily, ~4 joints/day).

• 12 non-users.No differences in CDS or driving performance.

Limitations

Small sample sizes.Did not measure withdrawal symptoms or reaction time.Simple lab-based simulation limits real-world application.

Key Findings

No dose-dependent or residual effects on driving after abstinence.Blood THC levels unreliable for impairment in regular users.Heavy users performed as well as non-users.

Implications

Challenges policies relying on blood THC for impairment.Suggests need for complex driving tasks in future studies.Supports rethinking cannabis intoxication laws.

Quotes

“No relationship between driving performance and cannabis use history or blood THC.”— Kyle Mastropietro, study author (UC San Diego).

“THC detectable long after use, not a reliable impairment indicator.”— Thomas Marcotte, PhD, senior author.