Latest Trends in US Marijuana Use Released

Pauline Anderson

Marijuana use increased among US residents from 2002 to 2014, and there was a drop in the number of American adults who believe the drug causes harm. In addition, there was no reported increase in marijuana use disorders, new research shows.

Understanding trends related to marijuana use "is relevant for policy makers who continue to consider whether and how to modify laws related to marijuana and for health-care practitioners who care for patients using marijuana," the authors, led by Wilson M. Compton, MD, National Institute on Drug Abuse, National Institutes of Health, write.

The study was published online August 31 in the Lancet Psychiatry.

Researchers examined data from adults who participated in the annual National Survey on Drug Use and Health (NSDUH), carried out by the Substance Abuse and Mental Health Services Administration.

NSDUH collected data on use of marijuana and other drugs during the previous 12 months as well as on recent heavy alcohol use. Participants were asked how much did people risk harming themselves when they smoke marijuana once or twice a week. They were also queried about perceived state legislation related to medical marijuana.

The data on marijuana use and related disorders collected from 2002 to 2014 allowed the researchers to examine when changes in trends started.

On the basis of the responses of the 596,500 adults sampled, the prevalence of marijuana use increased from 10.4% in 2002 to 13.3% in 2014. The upward trend started in 2007 (P < .0001).
The prevalence of daily or near-daily use of marijuana increased from 1.9% in 2002 to 3.5% in 2014; again the upward trend started in 2007 (P < .0001).

The surveys suggest that the prevalence of marijuana use is higher in non-Hispanic black people than in non-Hispanic white people. This contrasts with previous research and suggests "a shifting pattern of marijuana use in the USA," the authors note.

The prevalence of perceiving great risk for harm from smoking marijuana decreased from 50.4% in 2002 to 33.3% in 2014. Although the reduction started in 2003, it began to accelerate in 2007 (P < .0001).

Marijuana use was more prevalent in those living in states with legislation pertaining to medical marijuana. The prevalence of perceiving that medical marijuana was legal in their state increased from 17.9% in 2002 to 32.6% in 2014, with the upward trend starting in 2004 (P < .0001).

According to the authors, laws surrounding marijuana may help explain changes in marijuana use and the perception of the risk from such use. By 2007, 12 US states had legalized medical marijuana.

The survey did not find an increase in marijuana use disorders, which remained stable at about 1.5% (P = .22). Marijuana use disorders were associated with depression and the use of tobacco and other substances.

"Such co-occurrences are a stark reminder that marijuana use disorders are often comorbid with psychiatric illness and co-occur with use of multiple substances," the authors note. "When one of these psychiatric and behavioral problems is identified, clinicians must carefully look for other related problems."

The investigators also found that as marijuana use increased and marijuana use disorders remained stable, the available marijuana became more potent.

"We speculate that the many people who have recently (within the past year) started to use marijuana might be using the drug less intensely and have less psychopathology than people who have used marijuana for longer, which could decrease their risk of transition from use to use disorders," they write.

Future research on trends in marijuana abuse and dependence "could help elucidate reasons for the discrepancy between marijuana use patterns and use disorders," they add.

Previously, the National Epidemiologic Survey on Alcohol and Related Conditions found that there was an increase in marijuana use disorders among adults ― almost doubling from 2001 to 2012.

Differences in study design might explain the different findings. For example, the investigators point out that the current design provided respondents with relative privacy during in-person interviews at their residences, financial incentives, and several language choices, and so may have made them more willing to self-report substance use behaviors.

The study had a number of limitations. For example, it excluded the homeless and those living in institutions, and it could not reflect associations between marijuana use and specific psychiatric disorders. Because the data were cross-sectional, it was not possible establish causal relationships, and because the data were self-reported, they were subject to recall bias.