Accurate identification of opioid overdose deaths using coronial data

•Greater capture of opioid overdose deaths using Medical Cause of Death (MCOD) not ICD.•Investigative reports important to distinguish morphine from heroin & codeine deaths.•Toxicology results alone yields underestimates in heroin and codeine related deaths.•Investigative reports important for context (e.g. history of problematic substance use) of deaths.•Reports also important for extramedical use e.g. substance injected, syringes found. Defining drug-related mortality is complex as these deaths can include a wide range of diseases and circumstances. This paper outlines a method to identify deaths that are directly due to fatal opioid toxicity (i.e. overdose), utilising coronial data. The National Coronial Information System (NCIS), an online coronial database containing information on all deaths that are reported to a coroner in Australia, is used to develop methods to more accurately identify opioid overdose deaths. The NCIS contains demographic information, Medical Cause of Death, and associated documentation on toxicology, clinical and police investigations. Identifying overdose deaths using the coroner determined Medical Cause of Death provided greater capture, and specificity, of opioid overdose deaths. Distinguishing morphine from heroin-related deaths presented challenges, requiring analysis of clinical and investigative information in addition to toxicology results. One-quarter of the deaths attributed to morphine were recorded to heroin as a result of further investigation. There was also some underestimation of codeine-related deaths. Access to clinical and investigative information also yields important information in relation to comorbid conditions among these decedents, such as history of chronic pain, substance use issues and mental health problems. Reliance on toxicology results alone leads to an underestimate of heroin-related deaths. Differentiating between heroin and pharmaceutical opioid (e.g. morphine) overdose deaths has important public health and policy implications, particularly in relation to prescribing practices and development of a strategic response. Understanding comorbidities among these decedents is also important in efforts to reduce preventable causes of death such as opioid overdose.