The percentage of Americans who reported using marijuana in the past year more than doubled between 2001-2002 and 2012-2013, and the increase in marijuana use disorders during that time was nearly as large. This latest research also showed that 2.5 percent of adults — nearly 6 million people — experienced marijuana use disorder in the past year, while 6.3 percent had met the diagnostic criteria for the disorder at some point in their lives.