The Czar’s latest reefer faux pas? According to a previous, widely distributed ONDCP press release: “Marijuana affects … many of the skills required for safe driving. … These effects can last up to 24 hours after smoking marijuana.” 

Twenty-four hours, huh?  Well, an Israeli investigative team recently tested Walters’ claim — giving subjects high and low doses of THC and then measuring their driving performance.  Their conclusion, “No THC effects were observed after 24 hours on any of the measures.” 

This finding is not to say that concerns regarding motorists — especially teens — driving after smoking marijuana are not without merit. For example, the study’s authors found that pot, even at low doses, impaired drivers’ ability to maintain lane position and significantly increased subjects’ reaction time.

Intriguingly, however, the investigators reported that marijuana’s most prominent impact on driving differed dramatically from that of alcohol.

“Average speed was the most sensitive driving performance variable affected by both THC and alcohol but with an opposite effect,” authors concluded. “In particular, subjects seemed to be aware of their impairment after THC intake and tried to compensate by driving slower; alcohol seemed to make them overly confident and caused them to drive faster than in control sessions.”

To hear my expanded thoughts on this study, check out NORML’s 5/19/08 podcast here, or download a copy of NORML’s report, “Cannabis and Driving: A Scientific and Rational Review,” available here.