Marijuana is the world's most popular illicit drug, with hundreds of millions of users worldwide. One in three Americans has smoked pot, and in fact, the DEA estimates that Americans smoke five million pounds of marijuana each year. Nonetheless, marijuana remains largely misunderstood by both its advocates and its detractors. To some, marijuana is an insidious "stepping-stone" drug; to others, medical marijuana is an organic means of easing discomfort;...