The estimated prevalence of adults who used marijuana in the past year more than doubled in the United States between 2001 and 2013 to 9.5 percent, according to a new article. As is the case with alcohol, many individuals can use marijuana without becoming addicted. However, the clear risk for marijuana use disorders among users (approximately 30 percent) suggests that as the number of U.S. users grows, so will the numbers of those experiencing problems related to such use.