Our analysis of multiple national data systems indicates that cannabis use is associated with 83% increased odds of suicide. This finding is consistent with the Han et al. study (Han, et al., 2021), in which the prevalence of suicidality for cannabis users was significantly higher than for cannabis non-users among NSDUH respondents. The validity of our finding that there exists a robust association between cannabis use and increased suicide risk is further bolstered by the corroborative evidence that reaffirms several well-established risk factors for suicide, such as alcohol use, male sex, non-Hipanic White race, and less education attainment (Flensborg-Madsen et al. 2009; Borges et al. 2017; Peterson et al. 2020).

Our study contributes empirical evidence to the growing body of research linking cannabis use to increased suicide risk. Numerous studies have demonstrated a strong association between cannabis use and the development of psychotic disorders, such as schizophrenia (Volkow et al. 2014) and depression (Lev-Ran et al. 2014). These mental health issues can directly influence suicidal behavior, exacerbated by additional factors such as relationship problems, lower career achievement, and reduced life satisfaction. Furthermore, chronic cannabis use has been linked to cognitive and motor impairments, which may disrupt daily functioning and independence. For instance, impaired motor skills and slowed reaction time can affect driving ability, sometimes resulting in driving cessation—a loss of autonomy that has been associated with increased depression and suicide risk (Chihuri et al. 2016; Ko et al. 2021).

This study has several notable strengths. First, we used the case-control design and integrative data analysis techniques, including a novel data fusion approach to handling missing toxicological testing data. Selecting cases and controls from nationally representative samples enhances the generalizability of our findings compared to studies conducted in specific geographic regions or population groups. Additionally, by incorporating toxicological testing results instead of relying on self-reported data to determine cannabis use exposure, we minimized misclassification bias.

Several limitations should be taken into consideration when interpreting the study results. First, all toxicological testing data for NSDUH controls were imputed using prediction models trained on NRS data. This approach assumes that the relationship between self-reported and toxicology-confirmed use of cannabis and alcohol is consistent across populations. Differences in reporting behavior, such as underreporting in roadside survey settings, may limit calibration of the imputation model and underestimate uncertainty. Second, as NRS data cannot be disaggregated to state level, we could not restrict the analysis to the 17 states participating in the 2013 NVDRS. Differences in cannabis policy across states may therefore contribute to residual confounding. Also, our study may have limited applicability to certain racial and ethnic minorities due to inadequate representations in the study samples. Third, despite leveraging data fusion and multiple imputations to mitigate inaccuracies in self-reporting, selection bias might still be present due to the sampling methodology employed by NRS that targeted specific time windows on weekends. Fourth, the high prevalence of missing toxicological testing data on cannabis use from the NRS dataset may affect the accuracy of the multiply imputed data, as demonstrated in the discrepancies in the odds ratios derived from models before and after imputations using NRS data (Table 3). Fifth, our study results are susceptible to unmeasured confounding as some confounding factors, such as substance use disorder and history of depression and other mental health problems, are not accounted for due to the lack of data. Psychiatric conditions, such as major depression, schizophrenia, and anxiety disorder, have been recognized as important risk factors for suicide (Harris and Barrachlough 1997; Reutfors et al. 2009; Rivlin et al. 2010), and have been found to be positively associated with cannabis use (Bovasso 2001; Patton et al. 2002). Finally, this study does not assess the dose-response relationship between cannabis use and suicide because it is not feasible to multiply impute quantitative cannabis data.