Cannabis is now the most frequently detected illicit drug in drivers involved in motor vehicle crashes. Experimental research and epidemiological data have demonstrated psychomotor impairment associated with THC intoxication and quantified impairment with heightened risk of motor vehicle fatalities. Experimental laboratory studies have repeatedly demonstrated that the primary component of cannabis, Δ9-tetrahydrocannabinol (THC), impairs psychomotor skills including reaction time, focus, executive function, decision making, impulse control, and short-term memory, all important assets needed for safe driving.

Research reveals that the high from marijuana peaks during the first hour after smoking and slowly declines over the following 2 to 5 hours (Hartman and Huestis 2013), sometimes longer. Studies of aircraft pilots who failed to safely execute an emergency landing 24-hours after smoking marijuana should have been the wake-up call we needed regarding the prolonged impairment, in some case 1-2 days after the subjective “high” wears off. But well-financed proponents of marijuana legalization were successful at circumventing the conventions of scientific inquiry to assess safety and efficacy, thus allowing a largely uneducated public to vote the use of this addictive drug into law. As a result, the prevalence of cannabis use is expected to increase as ongoing legalization of both medical and recreational use proceed, despite any scientific evidence regarding the efficacy as a medicine or individual and public safety concerns 

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