Heavy Cannabis Use Alone Predicted Depression but Not Suicidality in High School Students Over 2 Years | Research

The takeaway

Among 976 Nova Scotia high school students followed for 2 years, heavy cannabis use alone predicted depression but not suicidal thoughts or attempts, while illicit drug use (with or without cannabis) predicted all three outcomes.

Read this if you are a parent or teen concerned about the mental health effects of cannabis versus other drug use.

Heavy cannabis use predicted depression but NOT suicidal ideation or attempts

What the researchers found

Nine hundred seventy-six students surveyed in grade 10 and again in grade 12 were assessed for cannabis, illicit drug use, depression, suicidal ideation, and suicide attempts. Illicit drug use (drugs other than cannabis), with or without cannabis co-use, was significantly associated with depression, suicidal ideation, and suicide attempts.

Heavy cannabis use alone (without other illicit drugs) predicted depression but not suicidal ideation or attempts. This distinction suggests that cannabis has a specific relationship with depressive symptoms, while the broader suicidality risk is driven more by general illicit drug involvement.

Why it matters

The differentiation between cannabis-specific and general illicit drug effects is clinically important. Cannabis alone appears to increase depression risk but not suicide risk, while polysubstance use involving illicit drugs is a stronger marker for suicidality. This helps clinicians calibrate their concern based on substance use patterns.

The numbers in context

976 students, grades 10 to 12, 2-year follow-up. Illicit drug use: significant for depression, suicidal ideation, suicide attempts. Heavy cannabis use alone: significant for depression only. Not significant for suicidal ideation or attempts.

How the study worked

Longitudinal study of 976 students in 4 Nova Scotia high schools. Assessed in grade 10 (2000-2001) and grade 12 (2002-2003). Generalized estimating equations modeled depression, suicidal ideation, and suicide attempts among drug users and non-users.

What this study cannot tell us

Relatively short follow-up (2 years). Self-reported substance use and mental health outcomes. "Heavy cannabis use" was defined by the study but details are not in the abstract. The sample was from a specific region that may not generalize. Confounding factors may explain the cannabis-depression link.

How to read the evidence

Longitudinal cohort with repeated measures; moderate evidence for distinguishing cannabis-specific from general drug-related mental health effects.

When this study was published

Published in 2013. The cannabis-depression relationship continues to be actively researched.

The bigger picture

This study supports the growing evidence that cannabis has a specific relationship with depression that is distinct from the broader substance use-suicidality link. It suggests that prevention efforts for cannabis-using teens should focus on mood monitoring, while polysubstance use requires more intensive suicidality screening.

Questions still open

Does cannabis cause depression or do depressed teens use more cannabis? Would the distinction between cannabis and illicit drug effects hold with longer follow-up? Could treating depression in cannabis-using teens reduce their cannabis use?

Common questions

Does cannabis cause depression in teenagers?

This study found that heavy cannabis use predicted depression over 2 years, but not suicidal thoughts or attempts. This association could mean cannabis causes depression, depressed teens use more cannabis, or shared risk factors drive both. What is clear is that heavy cannabis use in teens is a marker for depression risk, regardless of the direction of causation.

Is cannabis use related to teen suicide?

In this study, cannabis use alone was not significantly associated with suicidal ideation or attempts. However, illicit drug use (with or without cannabis) was significantly associated with all suicidality measures. This suggests that the suicide risk comes more from polysubstance involvement and the broader pattern of illicit drug use rather than from cannabis specifically.

Read the original research

Longitudinal associations of cannabis and illicit drug use with depression, suicidal ideation and suicidal attempts among Nova Scotia high school students.

Drug and alcohol dependence, 129(1-2), 49-53

View on PubMed ↗Publisher’s paper ↗

Citation

Rasic, Daniel; Weerasinghe, Swarna; Asbridge, Mark; Langille, Donald B. (2013). Longitudinal associations of cannabis and illicit drug use with depression, suicidal ideation and suicidal attempts among Nova Scotia high school students.. Drug and alcohol dependence, 129(1-2), 49-53. https://doi.org/10.1016/j.drugalcdep.2012.09.009