According to study published this week, the percentage of American adults who use marijuana more than doubled between 2002 and 2012. In my latest Forbes column, I explain why that news is not as alarming as the press coverage implied:
It stands to reason that legalizing marijuana, by making it easier, cheaper, and less risky to obtain, would encourage consumption. That is mostly a positive development, since it implies greater consumer satisfaction as more people enjoy a product that prohibition made harder to get. But it also stands to reason that as marijuana consumption rises, so will marijuana-related problems. The extent of those problems is a big part of the current debate about the wisdom of emulating Colorado, Washington, Oregon, and Alaska by treating marijuana suppliers as legitimate businesses instead of criminal organizations.
Contrary to what prohibitionists tend to assume, the increase in marijuana-related problems following legalization may not be proportional to the increase in consumption. It's plausible that people prone to excess are less likely to be deterred by prohibition than people of more moderate habits. If so, problem users may represent a smaller share of cannabis consumers after legalization than they did before, which means marijuana's benefit-to-cost ratio would improve. A study published yesterday by JAMA Psychiatry provides some evidence that as the number of cannabis consumers increases, the percentage who experience serious cannabis-related problems will decline.
That is not the way most news outlets presented the study's results. "Marijuana use has more than doubled in the U.S. since the beginning of the century," NBC News reported, "but so have problems for users." Reuters' gloss was similar: "As attitudes and laws in the US have become more tolerant of marijuana, the proportion of adults using and abusing the substance at least doubled between 2001 and 2013." Under the headline "Marijuana Use—and Abuse—in the U.S. Has Doubled in the Last Decade," Newsweek declared that "marijuana use disorders are now a bigger problem than ever." These alarming reports not only exaggerate the bad news in the study; they overlook the good news.