Duration of cannabis impairment
New analysis from the Lambert Initiative defines durations of impairment after inhaled or oral THC doses. Findings raise questions about current drug-driving laws, which penalise for THC presence, not intoxication levels.
A comprehensive analysis of 80 scientific studies has identified a ‘window of impairment’ of between three and 10 hours caused by moderate to high doses of the intoxicating component of cannabis, tetrahydrocannabinol (THC). The findings have implications for the application of drug-driving laws globally, researchers say.
The study found the exact duration of impairment depends on the dose of THC, whether the THC is inhaled or taken orally, whether the cannabis user is regular or occasional and the demands of the task being undertaken while intoxicated.
The study represents the first such meta-analysis and distilled the results of 80 separate scientific studies into THC-induced impairment conducted over the past 20 years. It has been published in Neuroscience & Biobehavioral Reviews.
“Legal cannabis use, both medical and non-medical, is increasingly common across the world,” said lead author Dr Danielle McCartney from the Lambert Initiative for Cannabinoid Therapeutics at the University of Sydney.
“THC is known to acutely impair driving and cognitive performance but many users are unsure how long this impairment lasts and when they can resume safety-sensitive tasks, such as driving, after cannabis consumption.
“Our analysis indicates that impairment may last up to 10 hours if high doses of THC are consumed orally. A more typical duration of impairment, however, is four hours, when lower doses of THC are consumed via smoking or vaporisation and simpler tasks are undertaken (e.g., those using cognitive skills such as reaction time, sustained attention and working memory).
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