The public health impact of legalizing marijuana for recreational use is concerning to some, but there is little evidence to back up these worries, experts say.

In fact, the passage of new laws in Colorado and Washington essentially amounts to a public health experiment, which researchers can use to gather information on the real harms and benefits of legalizing the drug in the United States, experts said. The laws, passed by voters on Tuesday, allow adults over age 21 to possess or buy up to 1 ounce of marijuana for recreational use.