Illegal Marijuana Use, Abuse Rising in States With Legalized Pot, Study Says

Nationwide data suggests illegal marijuana use increased at a "significantly greater rate" in states with medical marijuana laws, according to the study.

By Megan Trimble,

As of November 2016, 28 states had passed medical marijuana laws. (Katarzyna Bialasiewicz via Getty Images)

New findings suggest illegal pot smoking and abuse of the drug are on the rise in states that have legalized medical marijuana – and at a faster rate than in states that have held off on passing similar laws.

A team of researchers reported Wednesday that nationwide data suggests marijuana use and marijuana use disorders – in which people use the drug in unhealthy or abusive ways – increased at a "significantly greater rate" in states with medical marijuana laws than in states without the laws, according to the findings published online in the journal JAMA Psychiatry.

Twenty-eight states had passed medical marijuana laws as of November 2016, according to the study.

Researchers analyzed data surveyed from nearly 118,500 participants in 39 states between 1991 and 1992, 2001 and 2002 and 2012 and 2013. The rates of illegal pot use increased in all of those states over the course of the study, according to the findings.

The rates of illegal pot use rose from 4.5 percent to 6.7 percent, an increase of 2.2 percentage points, in states without medical marijuana laws. But illicit use rose in states with legalized medical marijuana from 5.6 percent to 9.2 percent, an increase of 3.6 percentage points, according to the study.

Researchers flagged California and Colorado as states that were notable for the reported increase in pot use. Both states have legalized the use of recreational marijuana since the period covered by the study data.

The study also found marijuana use disorders increased more quickly in states that legalized medical marijuana. States without legalized medical marijuana saw an increase in reported disorders from 1.3 percent to 2.3 percent, an increase of 1 percentage point. In states that have passed medical marijuana laws, the disorders rose from 1.5 percent to 3.1 percent, an increase of 1.6 percentage points.

But while the study found the disorders generally increased in adults, other studies have found a decline in the same disorders in teens between 2002 and 2013.

Researches noted a number of limitations in their study, including possible inaccuracies tied to the self-reported data. Some recreational marijuana users, for example, may feel more comfortable reporting their use today than people in the past. Additional studies, after all, have found that most Americans have tried marijuana.

Ultimately, researchers said, more studies are needed to explain why increased pot use could be linked to medical marijuana laws.