Sex differences in depression and substance use disorder diagnoses and overdose risk in British Columbia

Background: Depression is a risk factor for overdose and is more commonly diagnosed among females. However, sex-differences in the association between depression, in isolation and in combination with substance use disorder (SUD), and overdose have not been examined at the population level in British Columbia (BC). This study described sex-and-age differences in associations between documented history of depression and/or SUD diagnoses and risk of fatal (FOD) and non-fatal overdose (NFOD). Methods: This study used linked administrative health data from the Provincial Health Services Authority Platform for Analytics and Data. The sample included BC residents aged 19-79 as of January 1st, 2015 (n=3,996,690). Exposures were classified as documented diagnosis history of 1) depression; 2) substance use disorder (SUD); 3) depression and SUD; and 4) neither condition, using physician billing and hospitalization records from 2010-2014. FOD (BC Coroners Service records) and NFOD (BC Emergency Health Services records) were ascertained from 2015 to 2024. Incidence rates per 10,000 person-years and unadjusted incidence rate ratios (IRRs) and 95% confidence intervals (CI) were estimated using Poisson regression, with neither diagnosis as reference, overall and stratified by sex and age. Results: There were 14,281 FOD (78.59% male) and 43,555 NFOD (69.45% male) cases. FOD incidence was higher among males overall; however, relative associations between diagnosis history and FOD risk were stronger among females. Depression diagnosis history was associated with a FOD IRR of 3.95 (CI: 3.56-4.38) among females and 2.46 (CI: 2.32-2.61) among males. IRRs for SUD and for depression and SUD were larger among females (108.07 [CI: 95.83-121.73] and 116.70 [CI: 106.51-127.96]) than males (26.69 [CI: 25.57-28.18] and 31.21 [CI: 29.81-32.67]). NFOD findings were similar but attenuated (depression IRR: 3.22 [CI: 3.08-3.38]) in females; 2.29 [CI: 2.21-2.37] in males). Conclusion: A documented history of depression and/or SUD was more strongly associated with FOD and NFOD risk among females, despite higher incidence overall among males. Future research should consider the potential role of other sociodemographic factors in explaining sex differences in associations between diagnosis history and overdose risk.