What’s described as the largest study of the relationship between cannabis use and anxiety to date has found a significant proportion of individuals who had an emergency department visit for cannabis use developed a new anxiety disorder within three years.
The study included over 12 million people living in Ontario, Canada, between 2008 and 2019 who had never previously received a diagnosis or treatment for anxiety and was based on health record data from ICES. ICES data has encompassed the majority of publicly funded administrative health services records for the Ontario population eligible for universal health coverage since 1986.
Among the findings, 12.3% of individuals had an emergency department (ED) visit or hospitalization for an anxiety disorder and 27.5% of individuals had an incident outpatient visit, ED visit or hospitalization for an anxiety disorder within three years of an ED visit for cannabis use. Rates were much higher than the risk in the unexposed general population of 1.2% for the former and 5.6% for the latter.
While a link between cannabis use and anxiety appears to have been established, the researchers also offer two alternative explanations for their findings.
One is individuals with an existing anxiety disorder who have not yet presented for care may have been self-medicating with cannabis in an attempt to alleviate symptoms. While THC, the intoxicating cannabinoid is thought to decrease anxiety at lower doses, it may increase it at higher doses. The non-intoxicating cannabinoid CBD appears to not contribute to anxiety and may decrease it.
The other alternative explanation are common risk factors such as genetic predisposition or adverse life experiences may increase the risk of both severe cannabis use and anxiety disorders.
While the researchers also detail “several limitations” of their study, it’s an area they say requires further attention.
“Cannabis use has rapidly increased in Canada over the past 15 years and there is a general sense that cannabis is relatively harmless or has health benefits,” says lead author Dr. Daniel Myran. “Our study cautions that in some individuals, heavy cannabis use may increase their risk of developing anxiety disorders.”
The study has been published in The Lancet.