Marijuana is the most commonly used illicit drug in the US, and new research reveals that its use is on the rise among adults. However, the authors say the rate of increase is much lower than the “doubling” previously reported, and there has been no rise in marijuana-related problems over the past decade.

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Though marijuana use in the US has risen since 2002, a new study suggests it has not doubled like previous research has reported.

First author Richard A. Grucza, PhD, a professor of psychiatry at Washington University School of Medicine in St. Louis, MO, and colleagues publish their findings in the journal JAMA Psychiatry.

Last October, Medical News Today reported on another study published in JAMA Psychiatry that claimed marijuana use among American adults more than doubled between 2001-2002 and 2012-2013, from 4.1% to 9.5%.

Additionally, that study reported an increase in the rate of marijuana use disorders – including abuse and dependence – during the same time period, from 1.5% to 2.9%.

The new study, however, suggests that such figures are inaccurate, which Grucza and colleagues believe is down to underestimation of how many adults were using the drug in 2002.

The researchers note that last year’s study used two face-to-face interviews – one conducted in 2002-2003 and one conducted in 2012-2013 – to gather data on marijuana use and related problems, and the first interview was carried out by US Census workers.

“Data from face-to-face surveys previously have been demonstrated to be more sensitive to social attitudes than data collected anonymously,” explains Grucza. “People may say one thing to an interviewer but something else on an anonymous computer survey, particularly when the questions deal with an illegal substance.”

He adds that because marijuana has been legalized in several states in recent years and there has been a reduction in the stigma surrounding it, a person who may have been uncomfortable revealing their use of the drug in 2002 is likely to have been more open about it a decade later.

For the new study, Grucza and colleagues collected data on marijuana use in the US between 2002-2013 using data from the National Survey on Drug Use and Health (NSDUH) – an annual, nationally representative, computerized questionnaire that gathers information on prevalence and trends of drug use.

The data the team assessed was for more than 450,000 adults aged 18 and older.

From their analysis, the researchers did identify an increase in marijuana use from 2002-2013, but it was not as high as the increase reported in last year’s study.

The new research found that marijuana use increased by around 20% between 2002-2013, from 10.5% to 12.5%, while the previous study noted an increase from 4.1% to 9.5% in the same period.

“It’s not surprising that marijuana use is on the rise – several states have legalized it for either medicinal or recreational use – but our data suggest that the use rate hasn’t come close to doubling,” notes Grucza.

Furthermore, the new study found there had been no change in the rate of marijuana-related problems – such as addiction – between 2002-2013, contrary to the doubling of such problems reported in the previous study.

Commenting on their results, Grucza says:

We’re certainly seeing some increases in marijuana use. But our survey didn’t notice any increase in marijuana-related problems. Certainly, some people are having problems so we should remain vigilant, but the sky is not falling.”

Earlier this month, MNT reported on a study that associated past and present marijuana use with poorer verbal memory in middle age.