Public Health and Safety

THC and Its Effect on Driving

Date: January 22, 2021

The December 1st, 2020 edition of JAMA (Vol. 324, No. 21) released the results of a study into impaired driving from the Netherlands titled, “Effect of Cannabidiol and Δ9-Tetrahydrocannabinol on Driving Performance” by T. Arkell ( The near year-long study examined the effects of vaporized cannabis products on safe driving performance. Of 41 potential participants,  26 individuals with a history of “occasional cannabis use”, were screened and selected to be part of this study. The term, “occasional cannabis use” was defined as less than twice a week in past 12 months or more than 10 lifetime exposures.

During the study, that focused on how well the drivers maintained lane position on a roadway, all drivers were administered marijuana that was either THC dominant (22% THC potency), Cannabidiol dominant (9% CBD potency), or a placebo. During and after the driving sessions blood was collected for analysis. Also, drivers provided their subjective feedback on their driving quality, sense of impairment, and confidence to safely operate a motor vehicle. Note: Of the 188 monitored drives by participants, 16 had to be stopped for safety reasons. 

Some of the findings for the drivers that used THC products, compared to the CBD and placebo drivers included:

  • A lower confidence level in their driving ability
  • A lower perception of their driving quality
  • A higher sense of impairment 

The study showed that: 

  • The THC drivers had greater difficulty in maintaining lane position up to 5-hours after use
  • The drivers who used a CBD dominant or a placebo product, demonstrated no significant differences in their performance

Read Time: 5-10 minutes

Image: Unsplash / G.Pierce