More than 20 million Americans on average use marijuana each month, making it the most popular street drug in the country. Nine states -- Oregon, Washington, Colorado, Alaska, Nevada, Maine, Massachusetts, California, Vermont -- and the District of Columbia have legalized recreational marijuana. Many other states are considering laws to make it legal.

The number of Americans who are in favor of legalizing recreational marijuana has       risen. More than 60% of people surveyed now support the idea. Most Americans don't think marijuana is harmful. Yet despite the increasing acceptance, marijuana use does have some risks.