Introduction: Naloxone is recommended for reversing opioid-associated respiratory depression. There is wide variability in emergency department (ED) practice patterns regarding naloxone use, dosing, and observation time post-administration. This study describes the naloxone practice patterns of ED physicians managing suspected opioid overdose patients. Methods: A retrospective chart review was conducted of adult patients (≥ 18 years) presenting to an academic tertiary care centre (consisting of two EDs with an annual census 150,000 visits) in 2017 with suspected opioid overdose who were administered naloxone in the ED. Patients were identified electronically and the following information was abstracted from patient charts: demographics, naloxone dosage and infusion initiation, disposition data, indications for naloxone administration, response to therapy, and adverse effects. Variability in initial and total dose was examined. Initial dose was also compared in those with cardiorespiratory compromise (CPR given, respiratory rate < 8, or desaturation below 89%) using independent samples median tests. Data was analyzed using standard descriptive statistics. Results: 113 patients met inclusion criteria. Indications for naloxone administration were: level of consciousness (50.5%), respiratory depression (4.0%), miosis (1.0%), a combination of factors (19.8%), or undocumented (24.8%). Median initial dose was 0.40 mg (IQR: 0.20-0.40 mg). Median total naloxone administered in the ED was 0.48 mg (IQR: 0.35-1.2 mg). The initial dose resulted in a response in 43.1% of patients, with 36.0% of responding patients later experiencing subsequent respiratory depression. 31% of patients received a naloxone infusion. Initial dose in patients with cardiopulmonary compromise was significantly different only comparing patients who received CPR versus those who did not (median 0.40 mg; IQR: 0.20-0.80 mg; P = 0.019). Four patients experienced emesis following naloxone. Median length of ED stay was 7.0 hours (IQR: 4.0-9.5 hours), and median hospital length of stay was 3.0 days (IQR: 1.0-5.0 days). Median ED observation time prior to discharge was 4.0 hours (IQR: 2.0-8.0 hours). Ultimate disposition home, to the ward, or to the intensive care unit was 47.1%, 42.2%, and 9.8% respectively (1.0% deceased). Conclusion: The dose and usage of naloxone by ED physicians in this study is variable. Further prospective studies are needed to determine the effective naloxone dosing strategy.