New study suggests medical marijuana legalization may be associated with higher rates of mental illness

RESEARCH TRIANGLE PARK, NC—There may be a link between medical marijuana laws and mental illness, according to a new study published today in the International Review of Psychiatry. In the first study of its kind, researchers at RTI International found that states with liberal medical marijuana laws had a higher prevalence of serious mental illness than states without medical marijuana laws.  

“While this study doesn’t establish a causal relationship between liberal medical marijuana laws and mental illness, it does demonstrate that different types of marijuana laws likely have different effects on public health. We should explore what is driving the relationship we found,” said Lauren Dutra, social scientist at RTI, and lead author of this study.

The study shows that between 2008 and 2015, states with liberal medical marijuana laws – those that allowed medical use of marijuana for many health conditions – had a significantly higher prevalence of serious mental illness than states without legal medical marijuana. On average, the prevalence of serious mental illness was about 2% higher in states with liberal medical laws relative to states without medical marijuana.

Adjusting for current marijuana use explained 66 percent of the relationship between liberal medical marijuana laws and serious mental illness. However, prevalence of serious mental illness still remained significantly higher in states with liberal medical marijuana laws than in states without legal marijuana. In contrast, there was no significant difference between states with restrictive medical marijuana laws – those that allowed medical use primarily for life-threatening or chronic conditions – and states without legal medical marijuana.

Medical marijuana legalization has expanded rapidly within the United States. Between 2010 and 2016 the number of Americans living in states where medical marijuana is legal almost doubled. The study used data from the National Survey on Drug Use and Health (NSDUH) to examine the relationship between medical marijuana laws and mental illness that interfered with daily functioning and relationships, also known as serious mental illness. Some examples of serious mental illness include depression or hallucinations that keep someone from working or anxiety that keeps someone from leaving the house.

“With many Americans lacking access to mental health care, it’s more important than ever to study all of the factors that influence mental health outcomes in the United States,” Dutra said.

RTI International is a leader in marijuana research. For more than 40 years, RTI researchers have investigated the chemistry and pharmacology of cannabinoids and have studied the biological effects of marijuana use and its effects on society. RTI’s most recent research on the social science aspects of marijuana use focuses on the increasing popularity of marijuana and the public’s shifting perspective on the substance, the need for better labeling and quality control to protect public health, and the risks and benefits associated with edible marijuana and how it compares to the use of other drugs.

For more information on RTI’s research in medical marijuana, visit www.rti.org/marijuana.