Accidental versus intentional drug overdose deaths: a national register linkage study

Background

Norway has one of the highest rates of drug overdose deaths in Europe. Less than a quarter of drug overdose deaths in Norway involve heroin. The objective of this study was to identify differences between individuals dying of intentional versus accidental overdose deaths, in terms of their sociodemographic characteristics, medical history, and prescription history for opioids and other medicines with addictive potential.

Methods

This data linkage study involved six nationwide health and population registers: The Cause of Death Registry, the Norwegian Prescription Database, the Norwegian Patient Registry, the Norwegian Registry for Primary Health Care, the Cancer Registry of Norway, and Statistics Norway. For all eligible study cases of overdose deaths (intentional vs. unintentional) among individuals aged ≥15 years that occurred during the study period (2011 to 2019), data from the national registers were linked using unique personal identification numbers. Logistic regression analysis was used to explore factors associated with intentional versus unintentional overdose deaths. Multivariable logistic regression was conducted to control for potential confounding variables.

Results

The study population consisted of N=2,181 individuals, among whom 1,818 (83.4%) died from accidental overdoses and 363 (16.6%) died from intentional overdoses during the study period. Individuals in the intentional overdose group were, on average, eight years older (mean = 48.8; SD = 14.9; vs. mean = 40.9; SD = 13.0), more frequently women with higher educational attainment and a history of previous suicide attempts, compared to accidental overdose deaths. Intentional overdose deaths were more commonly associated with a lifetime history of chronic pain and with depression in the year leading up to death. Conversely, accidental overdose deaths were more frequently linked to a lifetime history of mental and behavioral disorders related to psychoactive substance use. Postmortem blood samples more frequently revealed the presence of pharmaceutically available opioids among intentional overdose deaths (73.0% vs. 36.0%). In the 30-day period preceding death, a higher percentage of individuals in the intentional overdose group had been prescribed opioids (43.0% vs. 21.4%) and/or benzodiazepines (51.5% vs. 38.7%) compared to accidental overdose deaths. However, after adjusting for other variables, these differences were not statistically significant.

Conclusion

Intentional overdose deaths typically involve prescribed medications and are more prevalent among older individuals, particularly women, with a history of somatic or mental disorders. Our findings support the need for screening for suicidal intent in clinical practice as well as the development of tailored interventions.