Researchers tested frequent cannabis users 12–15 hours after smoking and found no significant differences in simulator performance versus non-users, even with THC still present.
A new study in the Journal of Cannabis Research takes aim at one of the messiest questions in cannabis policy: what, exactly, does “the morning after” look like when it comes to driving?
Researchers recruited 65 frequent cannabis users, defined as people who smoked at least four times per week, and compared them with 65 non-cannabis users matched for age and sex, plus driving experience, annual driving distance, and sleep patterns. Then they did something simple and specific: they brought the cannabis group in the morning after they used cannabis, roughly 12 to 15 hours after their last smoke, put them in a driving simulator, and measured how they performed.
The headline finding was straightforward. Across standard driving and a more demanding “dual task” scenario meant to add distraction, the cannabis group did not show statistically significant impairment compared to the control group after correcting for multiple comparisons. Measures like speed and following distance were also not meaningfully different between groups.
The most commonly cited “weaving” metric in this kind of work is SDLP, or standard deviation of lateral position. In this study, SDLP was actually higher in the control group than in the cannabis group in both standard and dual task conditions, but the difference was small and did not remain significant after correction.
Here’s the part lawmakers and courtroom arguments tend to circle in red marker: THC was still detectable. In the cannabis group, mean blood THC the morning after was 2.8 ng/mL (median 1.2), and oral fluid THC averaged 31 ng/mL. Yet the researchers found no meaningful relationship between THC concentrations in blood or oral fluid and driving behavior after correction for multiple comparisons.
That does not mean …
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Author: Javier Hasse / High Times
