After cannabis, 68.6% felt ready to drive. Were they?
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After cannabis, how long until you're really ready to drive?
In one UC San Diego trial, 191 regular cannabis users smoked THC or a placebo, double-blind, then drove a simulator again and again.
At 30 minutes, 45.6% of the THC group drove badly enough to count as impaired. By 90 minutes, 68.6% said they'd drive now. Their driving hadn't improved.
On average, the THC group drove like the placebo group again by about 4.5 hours.
Sources
Marcotte TD, Umlauf A, Grelotti DJ, et al. Driving Performance and Cannabis Users' Perception of Safety: A Randomized Clinical Trial. JAMA Psychiatry 2022;79(3):201-209. doi:10.1001/jamapsychiatry.2021.4037
What the study says
- “Perception of driving impairment decreased at 1 hour 30 minutes, despite no objective improvement in driving; on average, performance was indistinguishable from the placebo group at 4.5 hours.”
- “Based on a 15th percentile cut point in the distribution of CDS change scores from the placebo group, 57 of 125 individuals (45.6%) in the THC group would be classified as impaired at 30 minutes”
- “At 30 minutes, 57 of 120 (47.5%) in the THC group would drive in their current state; this number increased to 81 (68.6%) at 1 hour 30 minutes, 107 (90%) at 3 hours 30 minutes, and 110 (93.2%) at 4 hours 30 minutes”
- “Although there was hesitancy to drive immediately postsmoking, increasing numbers (81 [68.6%]) of participants reported readiness to drive at 1 hour 30 minutes despite performance not improving from initial postsmoking levels.”
- “Postsmoking driving simulations occurred approximately 30 minutes, 1 hour 30 minutes, 3 hours 30 minutes, and 4 hours 30 minutes after smoking.”
Where it falls short
One simulator study of regular users who smoked flower. Real roads, edibles and other doses may differ.
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