The annual trend of suicide rates from 2010 to 2021 in patients with cannabis use disorder - a national registry study.

Purpose: The temporal trend of suicide in patients with cannabis use disorder (CUD) is important to investigate, considering the recent increases in THC concentration in cannabis products. This study describes the annual suicide rates in patients with CUD from 2010 to 2021. To investigate if any change in suicide rate was specific to CUD, we compared these suicide rates with corresponding data for patients with alcohol use disorders (AUD) and other substance use disorders (SUDs).

Method: The study used a time series design. We used a national registry linkage between the Norwegian Cause of Death Registry and the Norwegian Patient Registry from 2010 to 2021, including patients with CUD (ICD-10 code F12), AUD (F10), or other SUDs (F11; F13-F16; F18-F19) who died by suicide, supplemented with the total number of patients treated with specific disorders to estimate the suicide rates. The trend was analyzed by comparing the annual suicide rate to 2010 and using Poisson regression, adjusting for gender, age, and mental disorders.

Results: We found increased annual incidence rate ratios for patients with CUD in 2018 (IRR = 2.14 (95% CI 1.14-3.99)) and onwards and an increasing time trend over the study period (IRR = 1.08 (1.05-1.12)). No increases in trends were found for AUD or other SUDs. The time trend for CUD was attenuated when adjusting for depressive or anxiety disorders (aIRR = 1.00 (0.92-1.08)) or other SUDs (aIRR = 0.96 (0.87-1.06)).

Conclusions: Increasing suicide rates were found in patients with CUD. Comorbid anxiety and depression or other SUDs, but not other mental disorders, could partly explain these results.