As states slowly start to legalize medical marijuana, a question that has remained unanswered is whether more access means more recreational use, too. A new study out today in JAMA Psychiatry says it does.
There are 29 states along with Washington, DC that now have medical marijuana laws on the books. And while a few studies have tried to determine how these laws affect illegal marijuana use, this new study is the first to use data collected prior to any medical marijuana laws to track changes in illegal use rates.
The researchers, led by Deborah Hasin, a Professor of Epidemiology at Columbia University, looked at data collected in three national surveys on alcohol and drug use from 1991 to 2013.
Between the first and third surveys, the researchers found that illegal marijuana use increased more in the states that passed the laws compared to those that didn't.
In states with medical marijuana laws, illegal marijuana use increased by 3.6 percent compared to a 2.2 percent increase in states without medical marijuana. Cannabis use disorders, as defined by the DSM IV, the American Psychiatric Association's mental disorder manual, increased by 1.6 percent and 1.0 percent in states with and without medical marijuana laws, respectively.
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The authors believe these findings point to a potential health hazard. "Medical marijuana laws may benefit some with medical problems. However, changing state laws—medical or recreational—may also have adverse public health consequences, including cannabis use disorders," Hasin said in a statement.,
But the authors of the study also note several limitations. The surveys were self-reported and they admit that more people might have been willing to report their own drug use as it became more socially acceptable.
It should also be noted that requirements for a cannabis use disorder—a condition far less dangerous and prevalent than other kinds of drug and alcohol abuse—have changed since the three surveys were conducted. In the DSM IV, cannabis abuse and dependence were separate disorders and neither withdrawal nor craving were criteria for a dependence diagnosis. In the latest version, abuse and dependence have been merged and withdrawal and craving added to the criteria list, changing who might fit the bill for having a disorder.
The DSM IV also required one of four criteria to be met for a cannabis abuse disorder diagnosis, one of which was substance-related legal problems, a criterion that has been removed in the latest version. Those surveyed who were diagnosed with a cannabis use disorder may have received a different diagnosis under the new standards.
"Future studies are needed to investigate mechanisms by which increased cannabis use is associated with medical marijuana laws, including increased perceived safety, availability, and generally permissive attitudes," said Hasin.