Daily Cannabis Use Shows Minimal Impact on Driving in New Simulation Study

Study Finds Daily Cannabis Users Show Little Driving Impairment in Simulated Tests

A recent study published in Traffic Injury Prevention has revealed that daily cannabis consumers show minimal driving performance changes after cannabis use—suggesting a developed tolerance to its impairing effects.

Researchers at the University of Colorado Anschutz Medical Campus used a driving simulator to evaluate performance among three groups: daily users, occasional users, and non-users. Daily consumers—some of whom used cannabis concentrates with THC levels averaging 78%—showed few psychomotor deficits when tested 20 and 80 minutes after consumption.

In fact, daily users demonstrated improvements in standard deviation of lateral positioning (SDLP), a key measure of lane control. Interestingly, both daily and occasional cannabis users drove more cautiously by reducing their speed, while non-users tended to increase speed over time.

Occasional users did exhibit slight declines in SDLP after using cannabis, but the changes were not statistically significant compared to the control group. The most notable result was that daily concentrate users had virtually no change in speed or lane control—indicating strong tolerance to the effects of cannabis.

The researchers also highlighted a critical takeaway: THC levels in the blood did not correlate with impaired driving performance. This supports the growing body of evidence suggesting that THC per se limits are not reliable indicators of impairment.

“These findings reaffirm that the presence of THC in blood is an inconsistent and largely inappropriate indicator of psychomotor impairment in cannabis consuming subjects,” said NORML’s Deputy Director, Paul Armentano.

The study concluded that impairment from cannabis was more apparent in those who used it less frequently, but even then, the effect size was small. This underscores how personal tolerance and variability make it challenging to create standardized cannabis impairment thresholds.