Marijuana use is on the rise. About 20 million people in the U.S. use marijuana, up from 15 million users ten years ago. Legal for recreational use in four states and legal for medical use in 25 states, eventually, it’s anticipated that pot will be legal everywhere. But, there’s only one problem. It remains illegal for U.S. federal purposes. Marijuana is listed as a Schedule I controlled substance under Federal law, the most tightly restricted category for illegal drugs.