Keen C, Kinner SA, Young JT, et al. - Researchers conducted this retrospective cohort study with the aim to determine the treated prevalence of mental illness, substance use disorder (SUD), and dual diagnosis among residents of British Columbia, Canada. In addition, they investigated the correlation between dual diagnosis and fatal and non-fatal overdose. They assessed 921,346 British Columbia residents (455,549 males and 465,797 females) aged 10 and older using linked health, income assistance, corrections, and death records. In this cohort, 176,780 (19.2%), 6,147 (0.7%) and 15,269 (1.7%) had a history of mental illness only, SUD only, and dual diagnosis, respectively. Findings overall suggest that in the past 5 years, one in five individuals had sought care for a substance use disorder or mental illness. Individuals with a mental illness alone were noted to be at an elevated risk of overdose, this was higher again in people with a substance use disorder alone, and highest in people with a dual diagnosis. People with substance use disorder only and people with a dual diagnosis exhibited similar adjusted hazard rates.