Turna J, Simpson W, Patterson B, Lucas P, Van Amerigen M. Cannabis use behaviors and prevalence of anxiety and depressive symptoms in a cohort of Canadian medicinal cannabis users. J Psychiatr Res 2019; 111L134-149

Why was this study conducted?

Although scientific evidence is limited, many people believe cannabis can be used to treat anxiety and depression.  To study the prevalence of medical cannabis use for the treatment of anxiety and depression and the experience of patients, McMaster University researchers examined online survey data from Canadian medical cannabis patients registered with a single licensed medical cannabis producer.  In total, 2,032 patients provided data, of which 30.6% reported they received their authorization for cannabis in order to treat a mental health condition (stress, anxiety, depression, post-traumatic stress disorder, or eating disorder). Of those who received their authorization to treat anxiety and completed all of the psychometric screening instruments (888 or 43.7% of the respondents), 63.4% screened positive for one or more form of anxiety disorder. The vast majority (99.5%) had used cannabis prior to receiving a medical authorization.  Prior to receiving their authorization, 55% had used medication and 20.5% participated in cognitive-behavioural therapy to treat their anxiety. Most (92%) reported cannabis improved their symptoms and 49% that it replaced a non-psychiatric or psychiatric medication.  About a third (35%) reported using less than 1 gram/day, 42% between 1 to 2 grams, and 23% 3 or more grams. The amount of cannabis used per day was higher for those who reported more severe symptoms of anxiety or depression.

What does this study add?

Although there is limited evidence for its effectiveness, the study suggests that many Canadian medical cannabis patients are using cannabis for mental health conditions. These individuals report experiencing clinical benefits and reducing the use of other medications. 

Is there anything else I should know?

Because this study is cross-section (one-time) and relies on patients’ self reports, it can only describe patterns of relationships and causation cannot be determined.  For example, respondents using more than three grams a day reported greater perceived benefit but also more severe anxiety and depression symptoms. It is unclear whether increased cannabis use is a response to more severe disease, reflects a greater need for treatment, or may be a symptom of a cannabis use disorder. Whether perceived positive effects are specific to cannabis or placebo effects and whether cannabis objectively reduced other medication use cannot be ascertained.  This type of evidence suggests the need for randomized controlled trials, which are the gold standard for testing medical treatments.  More research is needed to help understand how cannabis should be used in the treatment of anxiety and depression.


Author Details

The latest scientific evidence on this topic was reviewed by the Centre's leadership team. This research summary is written by Corinne Hodgson, DHealth, assessed for accuracy by Co-Director Dr. James MacKillop, PhD, an expert in addictions and mental health research. There are no conflicts of interest. Questions regarding this piece should be directed to Dr. James MacKillop (jmackill@mcmaster.ca).