Cases were defined using the International Classification of Disease, Tenth Revision (ICD-10) codes for mortality. The following codes were selected from the underlying cause of death field to identify poisonings/overdoses: X40-X49, Y10-Y19. All multiple cause of death fields were then used to identify an opioid-related death: T40.0, T40.1, T40.2, T40.3, T40.4, and T40.6.
The Massachusetts age-adjusted opioid-related death rate was provided by the Massachusetts Department of Public Health.
The national level data was extracted from the Centers for Disease Control and Prevention, National Center for Health Statistics Wonder Databases.