Analysis of trends and usage of ICD-10-CM discharge diagnosis codes for poisonings by fentanyl, tramadol, and other synthetic narcotics in emergency department data

•More specific ICD-10-CM synthetic opioid poisoning codes implemented October 2020.•A single code was split into three new codes, including one for fentanyl poisoning.•Usage and trends of the new codes were explored in emergency department data.•Emergency department visits for synthetic opioid overdoses increased significantly.•76% of visits for synthetic opioid overdoses were coded as involving fentanyl.