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 last week 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.
Examining data from two large surveys of adults conducted in 2001-02 and 2012-13, Columbia University psychiatrist Deborah Hasin and her colleagues found that the share of respondents who reported using marijuana in the previous year rose from 4.1 percent to 9.5 percent. Hasin et al. argue that "more permissive" marijuana "laws and attitudes" are largely responsible for this increase in cannabis consumption. But the same factors may also have made survey respondents more willing to admit marijuana use, in which case some of the increase would be illusory.
The increase in marijuana use Hasin et al. report, which is based on the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC), is much more dramatic than the increase seen in the National Survey on Drug Use and Health (NSDUH) during the same period. According to the latter survey, the prevalence of past-year marijuana use among Americans 18 or older rose from 10.5 percent in 2002 to 12 percent in 2012. Furthermore, the NSDUH found no increase in the prevalence of "marijuana use disorders," which according to the NESARC numbers rose from 1.5 percent to 2.9 percent. Hasin et al. say "the explanation of these different findings is not clear."
Although Hasin et al. report that the prevalence of marijuana use disorders in the general population nearly doubled, they found that the prevalence of marijuana use disorders among cannabis consumers fell from 35.6 percent in 2001-02 to 30.6 percent in 2012-13, a 14 percent drop. That's a potentially significant development, but before considering why it's important to understand what Hasin et al. mean by "marijuana use disorder."
To qualify for that label, a respondent needed to meet one of the four criteria for "substance abuse" laid out in the fourth edition of the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders (DSM-IV):
1. recurrent substance use resulting in a failure to fulfill major role obligations at work, school, or home;
2. recurrent substance use in situations in which it is physically hazardous;
3. recurrent substance-related legal problems; or
4. continued substance use despite persistent or recurrent social or interpersonal problems caused or exacerbated by the effects of the substance.
Hasin et al. also included respondents who met at least three of the DSM-IV criteria for the more serious diagnosis of "substance dependence": tolerance, withdrawal, "taking the substance often in larger amounts or over a longer period than was intended," or "having a persistent desire or unsuccessful efforts to cut down or control substance use."
The definition of "marijuana use disorder" used by Hasin et al. is broader than the definition in the current, fifth edition of the DSM, which requires meeting at least two of 11 criteria. (Those criteria now include craving but no longer include legal problems.) Cannabis consumers whom Hasin et al. deemed to have marijuana use disorders clearly cover a wide range. They would include, for example, pot smokers busted for possession ("substance-related legal problems"), pot smokers who drive or operate machinery while high ("substance use in situations in which it is physically hazardous"), and pot smokers whose spouses think they smoke pot too much ("interpersonal problems"). They would also include people whose lives had been seriously disrupted by excessive marijuana consumption but who nevertheless had trouble cutting back or quitting.
Hasin et al. do not say what the breakdown was in either survey, but it seems likely that less serious problems predominated. While they say around 30 percent of past-year cannabis consumers have marijuana use disorders, data from the National Comorbidity Survey suggest that 9 percent of cannabis consumers experience dependence at some point in their lives.
Although it's clear that the vast majority of people who use marijuana do not become addicted to it, Hasin et al. obscure that point: "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 US users grows, so will the number of those experiencing problems related to such use." It's not just that "many individuals can use marijuana without becoming addicted." As with alcohol, addiction is an unusual outcome; users typically don't become addicted. Hasin and her colleagues compound the confusion by conflating addiction with the broader category of marijuana use disorders.
Hasin et al. argue that their findings should inform the debate about marijuana legalization. "While many in the United States [58 percent of Americans, according to the latest Gallup Poll] think prohibition of recreational marijuana should be ended," they write, "this study and others suggest caution and the need for public education about the potential harms in marijuana use, including the risk for addiction." But their findings also suggest a potential benefit of legalization.
According to the NESARC numbers, during a period when about a dozen states legalized marijuana for medical use, several decriminalized possession of small amounts, and two legalized marijuana for recreational use, cannabis consumers became less likely to abuse the drug. The NSDUH numbers, although they diverge in other ways, show the same thing: Between 2002 and 2012, according to the figures cited by Hasin et al., the prevalence of marijuana use disorders among cannabis consumers fell by 17 percent, from 15 percent to 12.5 percent. As more states legalize marijuana during the next decade, it seems reasonable to predict that the percentage of cannabis consumers who experience problems as a result of their marijuana use will continue to decline.
I say that for a few reasons. First, fewer cannabis consumers will experience prohibition-related problems such as getting arrested or losing a job after testing positive for marijuana. Second, I suspect the people who are most inclined to abuse drugs are also the least inclined to abstain because the law says they should. Third, a more tolerant atmosphere is more conducive to teaching people about responsible drug use, both through modeling and through the sort of explicit instruction that Hasin and her colleagues seem to have on mind. "This information is important to convey in a balanced manner," they say, and I agree. But such balance is difficult to achieve under prohibition, which encourages a black-and-white, all-or-nothing attitude toward drugs.
Hasin et al. illustrate that problem by worrying about the decline in the percentage of Americans who believe regular cannabis consumption poses a "great risk," which they erroneously equate with "public beliefs that marijuana use is harmless." Compared to other activities that Americans enjoy, such as drinking or skiing, marijuana use does not pose a great risk, and saying so is not the same as saying it poses no risk at all. Researchers who call for "public education about the risks of marijuana use, presented in a reasonable, balanced manner," as Hasin and her colleagues do, should lead by example.
This article originally appeared at Forbes.com.