Daily Digit is the story behind the numbers that make our world work. Today we’re looking at the United States' illegal drug of choice: marijuana. With weed now legal in eight states and counting, stoner culture has seemingly emerged from the fringes of moldy basements and dorm rooms into the mainstream. 118 million Americans — including three of the last four presidents — admit to using cannabis in one form or another in their lifetime. Compared with other drugs, including heroin, cocaine, methamphetamine and hallucinogens, marijuana is by far the most popular illegal substance among otherwise law-abiding adults.