Marijuana is the most widely used illicit drug in Amer ica. Some 40% of the adult population has tried mari juana at least once. It is the third largest agricultural commodity in the nation and a $10 billion industry. In many areas of the country, marijuana production or sale is the largest moneymaker by far. In Florida, for ex ample, it ranks ahead of every business except tourism. It is also a widely misunderstood substance. An en tire generation of Americans grew up believing that marijuana was virtually risk-free. This belief persists, despite growing evidence of physical, psychological,...