"While not all marijuana users experience problems, nearly 3 of 10 marijuana users manifested a marijuana use disorder in 2012-2013," the researchers stated in the study's abstract. "Because the risk for marijuana use disorder did not increase among users, the increase in prevalence of marijuana use disorder is owing to an increase in prevalence of users in the US adult population."
As you might have noticed, the rise of weed in the US has coincided with public perception shifting in favor of the drug and law changes throughout the country. A majority of Americans supported legalizing marijuana in 2013, which was up from less than a third 11 years earlier, according to a report by The Washington Post. Now, recreational cannabis is legal in four states -- Alaska, Colorado, Oregon, Washington -- and the District of Columbia. Medical marijuana is legal in 23 states, plus D.C., per the report.
However, Deborah Hasin, a professor of epidemiology in psychiatry at Columbia University and lead author of the study, told WaPo it's not entirely clear why there's been such a massive increase in Mary Jane and that more research needs to be done. But, uh, who'd ever volunteer for that kind of research?