More US Adults Using Marijuana as Attitudes Change

Megan Brooks

September 01, 2016

With growing legal and social acceptance of marijuana, an increasing number of US adults are using it, and are using it more often, new research shows.

The findings, published online August 31 in Lancet Psychiatry, reflect data from 596,500 adults who took part in the annual US National Survey on Drug Use and Health (NSDUH) from 2002 to 2014.

The percentage of adults aged 18 years and older who said they used marijuana in the previous year rose from 10.4% in 2002 to 13.3% in 2014. The number of adults who first started using marijuana in the previous year increased from 0.7% in 2002 to 1.1% in 2014. Daily or near-daily use of marijuana (5 days or more per week) rose from 1.9% to 3.5% over the same period.

Extrapolating this to the US population, the number of first-time adult marijuana users increased from 823,000 in 2002 to 1.4 million in 2014, and the overall number of marijuana users jumped by 10 million, from 21.9 to 31.9 million. The number of daily or near-daily users rose from 3.9 million in 2002 to 8.4 million in 2014.

Attitude Adjustment

These increases were associated with a decrease in the proportion of adults who perceived "great risk of harm" from smoking marijuana once or twice a week, from 50.4% in 2002 to 33.3% in 2014, report Wilson M. Compton, MD, from the National Institute on Drug Abuse, Bethesda, Maryland, and colleagues.

Despite the fact that more adults are using marijuana, and are doing so more often, there has not been an increase in the incidence of marijuana use disorders, the team reports. However, the authors note that the study did not look at marijuana use among children and teenagers, nor did it look at the link between marijuana use and other more severe psychiatric disorders.

In the general adult population, the prevalence of marijuana use disorder held steady between 2002 and 2014, at about 1.5%, and the prevalence among adults who were using in the past year declined from 14.8% in 2002 to 11.0% in 2014.

Changes in marijuana use and risk perception generally began in 2006-2007, the authors point out. Many US states have relaxed policies toward marijuana use, with medical marijuana now legal in 25 states and recreational use by adults legal in four states.

They caution that the current study does not fully assess the impact of recent changes to state-level marijuana laws on widening use, and they encourage continued monitoring of marijuana use and use disorders at national and state levels.

"Understanding patterns of marijuana use and dependence and how these have changed over time is essential for policy makers who continue to consider whether and how to modify laws related to marijuana and for healthcare practitioners who care for patients using marijuana," Dr Compton said in a news release. "Perceived risk of marijuana use is associated with high frequency of use, suggesting the potential value for modifying risk perceptions of marijuana use in adults through effective education and prevention messages," he adds.

Too Soon to Draw Conclusions

It is "probably too soon to draw conclusions" about what impact marijuana policy changes are having on marijuana use and related harms, say Wayne Hall, PhD, University of Queensland, Australia, and Michael Lynskey, PhD, King's College London, United Kingdom, in a linked comment. But they say it is "likely" that these changes will increase the prevalence and frequency of marijuana use and, potentially, use disorders in the longer term.

"To investigate this possibility, the US needs to continue to monitor cannabis use and disorders in large scale surveys, such as the National Survey on Drug Use and Health and the Monitoring the Future national survey of high school students," Dr Hall and Dr Lynskey advise.

"Monitoring of cannabis use will need to address one of the major limitations of these surveys for this task, namely, that they were designed to provide nationally representative samples and do not necessarily provide representative samples of individual states. US federal funding agencies should consider funding oversampling of representative population samples within states that have and have not legalized cannabis for recreational and medical use," they suggest.

This study was jointly sponsored by the Substance Abuse and Mental Health Services Administration, the National Institute on Drug Abuse, and the Office of the Assistant Secretary for Planning and Evaluation of the US Department of Health and Human Services. The authors have disclosed no relevant financial relationships.

Lancet Psychiatry. Published online August 31, 2016. Abstract, Comment


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