Eye-opening new data on marijuana… A new Gallup Poll says the number of adult American pot smokers has nearly doubled in the last three years. According to the telephone survey of one-thousand people, that breaks down to one in eight people. A 2014 government study found cannabis to be the most commonly used illicit drug. The Drug Enforcement Agency lists marijuana as a schedule one drug — The same category as heroin. DEA officials say pot use has been linked to numerous physical and mental issues.