Dhivya Ramalingam, Ph.D.

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The problem: Depression affects millions of people worldwide and is associated with poor health outcomes, suicide and mortality due to other causes.

 

Why do this study? Because cannabis use has been associated with depression, it is important to know how regular cannabis use contributes to depression and thoughts of suicide.

The goal of this study was to define the associations between regular cannabis use and both depression and suicidal ideation, as well as changes in these associations over time.

 

The study: The study used mental health data from the 2002 and 2012 Canadian Health Surveys. Survey data were collected from a total of 43,466 individuals, aged 15-60. The main outcomes measured were suicidal thoughts in the past 12 months and depression. This study found that people who used cannabis at least monthly had about a 2x greater likelihood of depression and suicidal thoughts compared to non-users.  Also, those associations were stronger in 2012 than in 2002.  For instance, Canadians who used cannabis once a month in 2012 had 1.59 greater odds (a measure of association) of having suicidal thoughts compared to users in 2002.  Users had similarly greater odds of having depression in 2012 compared to 2002.

 

Conclusions: Monthly cannabis use was associated with an increased likelihood of suicidal thoughts and depression. This association was stronger in 2012 than it was in 2002.

 

What does this study add? The study suggests that suicidal thoughts and depression may increase with regular cannabis use, and that this association may be changing over time.

 

Funder: Canadian Institute of Health Research (CIHR)

 

Author conflicts: None

 

Commentary: This study raises more questions than it answers and that’s what makes it so interesting.  It’s a descriptive study, so it offers associations rather than causation. So cannabis use is associated with depression and suicidal ideation. Is cannabis use responsible for those outcomes?  Or are people who are depressed more likely to self-medicate with cannabis?  This study doesn’t prove the former is true—nor does it claim to.  But it does at least open that possibility, and that’s a possibility that we should take seriously.  And even if people are self-medicating for mental health symptoms, that would also be important to know, so we can provide more complete mental health services.  So this is a fascinating—albeit preliminary—study that offers a powerful argument for doing a prospective study that can tease out questions of causality.