Marijuana use among American adults doubled over a decade. That's according to government surveys showing that almost 10 percent of adults use the drug, or more than 22 million people.
Most of that is recreational use.
The researchers say the trend reflects a cultural shift and increasingly permissive views about the drug. Recreational use is now legal in four states.
Almost 1 in 3 users had signs of marijuana dependence or abuse. That's a slight decline from a decade ago.
The results come from a comparison of health surveys from 2001-02 and 2002-13 sponsored by the National Institute on Alcohol Abuse and Alcoholism.
Results were published Wednesday in the journal JAMA Psychiatry.