Cannabis Impairs Driving in Simulator Study, Even When Users Feel Fine | Research

The takeaway

A randomized driving simulator trial showed cannabis impaired key driving metrics even when participants did not feel significantly impaired.

Cannabis users who drive, traffic safety researchers, policy makers

Driving impairment detected even when participants felt capable of driving

What the researchers found

In a controlled simulator study, cannabis administration led to measurable driving impairment including lane weaving and reaction time delays, even when participants self-reported feeling capable of driving.

Why it matters

The disconnect between feeling capable and actually being impaired is a critical safety issue, especially as cannabis legalization expands and more people drive after using.

The numbers in context

Randomized trial with driving simulator; specific impairment metrics and THC doses in full text.

How the study worked

Randomized, controlled driving simulator study where participants received cannabis or placebo and completed standardized driving tasks while objective and subjective impairment were measured.

What this study cannot tell us

Simulator driving may not perfectly replicate real-world conditions. Acute dosing in a lab does not capture the full range of cannabis use patterns. Tolerance effects in regular users may differ.

How to read the evidence

Randomized controlled design provides strong internal validity, though simulator setting limits real-world generalizability.

When this study was published

2025 randomized controlled trial with current road safety relevance.

The bigger picture

Unlike alcohol, cannabis impairment is harder to self-detect. This gap between perceived and actual impairment complicates road safety efforts and public messaging about drugged driving.

Questions still open

How long after cannabis use does driving impairment persist? Can any self-assessment tool reliably help users gauge their fitness to drive?

Common questions

Can you tell if you are too impaired to drive after cannabis?

This study suggests not reliably. Participants showed measurable driving impairment on the simulator even when they reported feeling capable of driving safely.

How does cannabis affect driving ability?

The simulator study found cannabis caused lane weaving and slower reaction times, both key factors in real-world crash risk.

Read the original research

A randomized, placebo-controlled, double-blind, pilot study of cannabis-related driving impairment assessed by driving simulator and self-report.

Journal of psychopharmacology (Oxford, England), 39(4), 364-372

View on PubMed ↗Publisher’s paper ↗

Citation

Meda, Shashwath A; Stevens, Michael C; Boer, Erwin R; Pittman, Brian; Gueorguieva, Ralitza; Huestis, Marilyn A; Pearlson, Godfrey D. (2025). A randomized, placebo-controlled, double-blind, pilot study of cannabis-related driving impairment assessed by driving simulator and self-report.. Journal of psychopharmacology (Oxford, England), 39(4), 364-372. https://doi.org/10.1177/02698811251324379