Marijuana impairment will be difficult to prove and prosecute

In 2006, The Canadian Public Health Association made 55,000 copies of this poster and sent them out to high schools across the country to warn students against toking and driving. "With a drug that’s ingested in gummies, cookies, inhaled in many different ways, and available in all manner of potencies, good luck giving users any sense of how much is too much or how long they need to wait before they are competent to get behind the wheel," writes Ian Cooper.