Why should I wait 6-8 hours before driving?

Driving under the influence of alcohol is easy to test and measure because of breathalyzers – unfortunately these are not available yet for marijuana.  While a marijuana DUI can be verified through a blood test, that is less helpful for people wondering what that means about their ability to drive if they’ve recently used marijuana.  The importance of a three hour window is this — one published study (Grotenhermen, et al., 2007) shows that it takes 3 hours to drop below 4.9 nanograms of THC per milliliter of blood, meaning any driving within 3 hours of use would necessarily result in a person being above this cutoff.  That study was with marijuana from 2007, and, as potency has increased nation-wide and in Washington, it could take even longer. More recent studies suggest impairment can last 6-8 hours, especially for potent weed, edibles, and medical marijuana. Despite some people’s perception, there is no evidence in any studies that people “drive better” after marijuana use.