Study: Cannabis Impairment Lasts Between 3 and 10 Hours

Australian researchers at the University of Sydney’s Lambert Initiative for Cannabinoid Therapeutics suggest that cannabis impairment lasts, at most, 10 hours, and as little as three hours based on moderate to high doses. The researchers conducted a meta-analysis of 80 separate studies – as far back as 20 years – on how THC affects a person’s driving.

Danielle McCartney, the study’s lead researcher told LAD Bible that the “analysis indicates that impairment may last up to 10 hours if high doses of THC are consumed orally” but “a more typical duration of impairment … is four hours, when lower doses of THC are consumed via smoking or vaporization and simpler tasks are undertaken.”

The study, published in the forthcoming July issue of the journal of Neuroscience & Behavioral Reviews, suggests that the “results suggest individuals should wait at least 5 [hours] following inhaled cannabis use before performing safety-sensitive tasks.”

A study published last week by the U.S. National Institutes of Justice concluded that THC in biofluid markers “were not reliable indicators” of cannabis intoxication and that “standardized field sobriety tests commonly used to detect driving under the influence of drugs or alcohol were not effective in detecting” cannabis impairment.

That study, conducted by RTI International, found that for vaped THC doses exceeding 5 milligrams, “peak cognitive and psychomotor effects were observed zero to two hours after administration and returned to baseline after four hours.” For edibles, the peak effects were observed five hours after administration and functions returned to normal about eight hours after ingestion.