Marijuana Plant (IMAGE) Washington University School of Medicine Caption Washington University School of Medicine researchers report an estimated 12.5 percent of adults living in the United States use marijuana, but their research also shows that the rate of pot use did not double from 2002 to 2013 -- as had been reported in the fall -- but instead increased by about 20 percent. Meanwhile, the rate of problems related to the drug has remained steady. Credit B. DUNGEON Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.