Evidence of Marijuana's Health Effects Is Hazy At Best

"Colorado opened its first pot stores in January, and adults in Washington state will be able to walk into a store and buy marijuana this summer. But this legalization of recreational marijuana is taking place without much information on the possible health effects."

"'We should have been doing a lot more research to find out just how useful it is, how it affects the brain, et cetera, et cetera,' according to Dr. Herbert Kleber, a Columbia University psychiatrist and drug abuse researcher."

"But he says it's been hard to study the effects of Cannabis sativa, the plant that produces marijuana."