A groundbreaking study analysing health data from over 12 million residents of Ontario, Canada, has uncovered a significant association between emergency department visits for cannabis use and the development of new anxiety disorders revealing that there is a 3.7-fold increased risk of severe or worsening anxiety disorders.

The study, led by researchers at the Bruyère Research Institute, the University of Ottawa Department of Family Medicine, the Ottawa Hospital, and ICES, is the largest study to date examining the relationship between cannabis use and anxiety.

The research findings, published recently in The Lancet’s open-access journal eClinical Medicine, challenges prevailing notions of cannabis as a benign substance, shedding light on the complexities of its impact on mental health, emphasise the need for caution in both medicinal and recreational cannabis use, the researchers said.

The study revealed that cannabis use increased the risk of developing new anxiety disorders, with individuals seeking emergency care for cannabis use demonstrating a staggering 3.9-fold increase in the risk of being diagnosed with a new anxiety disorder within three years, compared to the general population.

It further revealed that there is a 3.7-fold increased risk of severe or worsening anxiety disorders following emergency department visits among cannabis users.

Alarmingly, 27.5 per cent of those who had an emergency department visit for cannabis use developed a new anxiety disorder within three years, compared to only 5.6 per cent of the general population, the researchers noted in the paper.

It further found that younger adults (10–24 years) and men were particularly at elevated risk, with individuals of all ages at a heightened risk of developing new anxiety disorders.

The extensive research suggests a potential causal relationship between cannabis use and increased anxiety, cautioning against its use as a treatment for anxiety symptoms.

Commenting on the findings, lead author Dr Daniel Myran, a Canada Research Chair in Social Accountability at the University of Ottawa and an ICES Adjunct Scientist highlighted the significance of the findings, saying, "Our study cautions that in some individuals, heavy cannabis use may increase their risk of developing anxiety disorders."

While debates persist regarding whether cannabis use directly causes anxiety disorders or if individuals self-medicate anxiety symptoms with cannabis, the authors emphasise the need for caution.

Regardless of causality, the study warns against using cannabis to treat anxiety symptoms, citing a lack of evidence for its efficacy, potential delays in evidence-based treatments, and the risk of worsening anxiety symptoms.

As cannabis use continues to rise in Canada, this comprehensive study adds a critical perspective to the ongoing discourse, urging a reconsideration of the perceived harmlessness of cannabis and underscoring the importance of informed decision-making in its use.