The proportion of people who reported smoking marijuana in the United States has doubled over 10 years, and almost one-third of users – 6.8 million people – are addicted, a new government survey has found.
“The important findings of the study is that the rates of use are going up,” said Deborah Hasin, lead researcher on the study released by the National Institute on Alcohol Abuse and Alcoholism, part of the National Institutes of Health (NIH). “[Marijuana is] not a completely harmless substance, and there are some risks involved.” Hasin said the takeaway should be that the number of people dependent on marijuana will increase with social acceptance.
Some scientists, however, question whether rates of marijuana use have gone up nearly as drastically as the study suggests.
“We are now a country that is much more liberal regarding marijuana use than we were 10 years ago, so it’s quite possible that in 2001-02, many more people underreported problems with marijuana use than they are reporting now,” said Raul Caetano, a University of Texas public health researcher who has received grants from the National Institute of Alcohol Abuse and Alcoholism.
“All these illegal behaviors, and undesirable behaviors, even including alcohol, are underreported in survey research. We know that. So to the extent that the country becomes more and more liberal … it becomes more and more OK to say, ‘Yes, I use’,” Caetano said.
The study published in the Journal of the American Medical Association (JAMA) Psychiatry compares two large population surveys, one from 2001-02 and another from 2012-13. More than 36,000 people were sampled, a scale almost exclusively achieved by government researchers. Both surveys were conducted through face-to-face interviews for the National Epidemiological Survey on Alcohol and Related Conditions (NESARC).
Researchers found the prevalence of past-year marijuana use more than doubled from 4.1% in 2001-02 to 9.5% in 2012-13. As a comparison, another major government study found that about 16.6% of American adults used marijuana in 2014.
The study also assessed rates of addiction and abuse. It found a substance use disorder rate, or what a layperson might call a substance abuse rate, of 2.9% among the general population, up from 1.5% in 2001. Among marijuana users, the substance use disorder rate was 30.5% – a rate far higher than what was found by past studies of marijuana addiction.
Marijuana is still far less widely used than substances that are legal everywhere in the US for adults. In 2014, NDUHS found 70.7% of Americans had used alcohol in the past year, and 32.6% had used tobacco. In the US population, the alcohol dependence rate was 9.6%, but it has been as high as 15% in other studies.
“I would think at least some of that [increase in marijuana use] is increased reporting, that adults feel more comfortable reporting, would be my first thought about that,” said California researcher Sheigla Murphy, who was awarded a more than $500,000 NIH grant to assess baby boomers’ attitudes on marijuana in the San Francisco Bay Area.
Hasin rejected the idea that changing social norms could explain the apparent increase in rate of users. Other studies questioned that assumption, pointing out that government workers (in the form of the US Census Bureau) conducted one of the surveys.
“To our knowledge, no formal research on the effect of interviewer affiliation on response to sensitive questions has been conducted, but one might speculate that respondents would be less forthcoming in surveys administered by government agencies,” a 2007 study published in the journal Addiction said.
The study is part of a suite of large-scale governmental research on prevalence. But, unlike other government measures, the study released on Wednesday found a marijuana addiction rate almost 20% higher than others.
The most comparable research, called the National Drug Use and Health Survey (NDUHS), found in 2013 that 9% of all people who smoked marijuana in the last year had a use disorder. NESARC found more than triple that – 30.5% of people that use marijuana depended or abused the drug in 2012-13.
NESARC did not compare addiction rates among substances, but the most widely cited study found about 32% of tobacco users became dependent, 23% of heroin users, 15% of drinkers and 9% of marijuana users. Those numbers are from the 1994 National Comorbidity Survey (released squarely within the “war on drugs” era).
Some addiction specialists have criticized the way NESARC diagnoses substance abuse, which includes standards abandoned by American psychiatrists.
“I call it an asocial addictionology,” said Sunil Aggarwal, an NIH-trained palliative care physician who studies medical marijuana use. “Not that there aren’t people out there who have problematic relationships with this.” Scientists often look at addiction studies as: “it’s the chemical, it’s the person, it’s the brain, and that is not really a scientifically – socially scientifically – valid human-cannabis relationship,” Aggarwal said.
In fact, researchers’ choice of methodologies for the survey “may have limited NESARC’s usefulness”, Caetano wrote in an editorial for the Society for the Study of Addiction, specifically because some questions may inflate findings.
One measure NESARC used to determine whether people are addicted to a substance has been particularly controversial: whether interviewees had legal troubles because of it.
Given that NESARC purposely oversamples black and Hispanic respondents, and that marijuana arrests are among the most common legal troubles for these demographic groups, scientists said it seems possible that these groups could skew rates. The American Psychiatric Association dropped the legal troubles marker in its updated DSM-5 handbook because of “cultural considerations”.
“[S]urvey respondents may misinterpret questions about some indicators of DSM-IV alcohol abuse and dependence [which serves as the same basis for questions about marijuana] which may artificially inflate the prevalence of these two conditions, especially in younger population groups,” the editorial said. DSM-IV’s diagnostic criteria also came under criticism, “because of the association between a positive diagnosis and individuals’ socio-economic status”.
In fact, those very groups were pointed to as significant by NESARC researchers.
“Groups in which the magnitude of increase was most notable included those aged 45 to 64 years (0.4% vs 1.3%); black individuals (1.8% vs 4.6%); Hispanic individuals (1.2% vs 2.8%); those with the lowest income (2.3% vs 5.4%); and those in the South (1.0% vs 2.6%),” researchers wrote.
The NESARC study does not assess the severity of marijuana-related dependence. While some studies have reported that abuse can lead to failure to fulfill obligations (such as school or work) or put people in dangerous situations (such as driving while high), other symptoms, such as withdrawal, remain mild compared even to prescription drugs such as opioid painkillers.
“Marijuana has been a recreational drug, or considered to be like wine or beer, those kinds of [substances], for a long time,” Murphy said. “It’s sort of a different category than all the sudden taking a Vicodin as a party drug – it has a different sort of history.”
Among marijuana legalization advocates, the study was viewed as another example of skewed politics infecting psychiatric standards.
“By any rational assessment, the continued criminalization of cannabis is a disproportionate public policy response to behavior that is, at worst, a public health concern,” said Paul Armentano, deputy director of the National Organization for the Reform of Marijuana Laws, known as NORML. “It should not be a criminal justice matter. These findings do little to change this fact.”
And the newest public opinion is on those advocates’ side. A Gallup poll released the same day as the study in JAMA Psychiatry found that 58% of Americans believe marijuana should be legal.
