Study: Marijuana Use Results in Decreased Speed, No Negative Effect, on Driving

According to a newly released study subjects who consumed cannabis typically decrease their driving speed and demonstrated few other significant changes.

The study, titled Acute and residual effects of smoked cannabis: Impact on driving speed and lateral control, heart rate, and self-reported drug effects, was published in the journal Drug and Alcohol Dependence.

For the study researchers had participants take part in a simulated driving performance after inhaling something with high-THC, something with low-THC, or a placebo. Performance was monitored 30 minutes after the inhalation took place. Additional examinations took place 24 and 48 hours after.

Smoked cannabis (12.5 percent THC) led to an acute decrease in speed in young adults,” states the study. They also note: “There was no clear effect of smoked cannabis on lateral control” and “There was no evidence of residual effects”.

Researchers conclude by stating that “Among young regular but non-dependent cannabis users, smoked cannabis led to a significant reduction in driving speed, …but there was little evidence of residual effects.”

The full abstract of the study can be found below:


Although driving under the influence of cannabis is increasingly common among young adults, little is known about residual effects on driver behavior. This study examined acute and residual effects of smoked cannabis on simulated driving performance of young cannabis users.


In this double-blind, placebo-controlled, parallel-group randomized clinical trial, cannabis users (1-4 days/week) aged 19-25 years were randomized with a 2:1 allocation ratio to receive active (12.5% THC) or placebo (0.009% THC) cannabis in a single 750 mg cigarette. A median split (based on whole-blood THC concentrations at the time of driving) was used to divide the active group into low and high THC groups. Our primary outcome was simulated driving performance, assessed 30 min and 24 and 48 h after smoking. Secondary outcomes included blood THC concentrations, subjective drug effects, and heart rate.


Ninety-six participants were randomized, and 91 were included in the final analysis (30 high THC, 31 low THC, 30 placebo). Mean speed (but not lateral control) significantly differed between groups 30 min after smoking cannabis (p ≤ 0.02); low and high THC groups decreased their speed compared to placebo. Heart rate, VAS drug effect and drug high increased significantly immediately after smoking cannabis and declined steadily after that. There was little evidence of residual effects in any of the measures.


Acutely, cannabis caused decreased speed, increased heart rate, and increases in VAS drug effect and drug high. There was no evidence of residual effects on these measures over the two days following cannabis administration.

1 thought on “Study: Marijuana Use Results in Decreased Speed, No Negative Effect, on Driving”

  1. Seems to me low grade pot and a very small sample group using a short term test is the same as minimizing having one drink. Pot does affect concentration and thinking. We dont need to minimize the effects of high grade pot and hash on drivers. There is no place for people to think it’s ok to drive high. It hasnt been legal long enough to to have truly legitimate study done and just take the driving part out permanently. I would think the lives booze and pills have taken in car deaths would have taught you not to push harmless thoughts about driving high. I smoke regularly and wont drive if I’ve smoked in the last ten hours.


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