ABSTRACT: INTRODUCTION:National data on morbidity from nonmedical use of pharmaceuticals are limited. This study used nationally representative, public health surveillance data to characterize U.S. emergency department visits for acute harms from nonmedical use of pharmaceuticals and to guide prevention efforts. METHODS:Data collected in 2016 from the National Electronic Injury Surveillance System-Cooperative Adverse Drug Event Surveillance project were analyzed in 2018 to calculate national estimates of emergency department visits for harms from nonmedical use of pharmaceuticals. RESULTS:Based on 5,130 surveillance cases, there were an estimated 358,247 emergency department visits (95% CI=280,675, 435,819) in 2016 for harms from nonmedical use of pharmaceuticals and 41.1% resulted in hospitalization (95% CI=32.3%, 49.8%). One half (50.9%, 95% CI=46.6%, 55.3%) of estimated visits involved patients aged ?34 years; more than one half of estimated visits also involved non-pharmaceutical substances (52.9%, 95% CI=49.7%, 56.1%), including illicit drugs in 34.1% (95% CI=30.9%, 37.2%) and alcohol in 21.8% (95% CI=19.8%, 23.9%). Overall, benzodiazepines were implicated in 46.9% (95% CI=42.5%, 51.2%) of estimated emergency department visits for nonmedical use of pharmaceuticals but were the only substance implicated in just 6.5% (95% CI=5.1%, 7.9%). Prescription opioids were implicated in 36.2% (95% CI=30.8%, 41.7%) of estimated emergency department visits and were the only substance implicated in 11.3% (95% CI=8.6%, 14.0%). CONCLUSIONS:Although prescription opioids or benzodiazepines are frequently implicated in emergency department visits for nonmedical use, because other substances and additional pharmaceuticals are most often involved, prescribing clinicians should consider implementing specific screening to address polysubstance use and, when warranted, treatment interventions.