Abstract Purpose Opioid analgesics are potent respiratory depressants. The purpose of this study was to describe the effects of opioids administered within 24 hours before cardiac arrest on clinical outcomes. Materials and methods We retrospectively collected the cardiac arrest data of noncancer patients who were admitted to the general ward of Asan Medical Center from January 2008 to August 2012. We investigated the proportion of these patients who received opioids within 24 hours of a cardiac arrest event, as well as the cardiac arrest characteristics, survival rates, and opioid administration patterns. Results Of the 193 patients identified, 58 (30%) had been administered opioids within the previous 24 hours (the opioid group), whereas the remaining 135 (70%) had not been administered opioids (the nonopioid group). The survival rate did not differ significantly between these 2 groups. In the opioid group, as-needed opioid administration was associated with a lower 24-hour survival rate than regular opioid administration (9 33.3% of 27 patients vs 20 64.5% of 31 patients; P = .030). In multivariate logistic regression analysis, as-needed opioid administration was negatively associated with 24-hour survival. Conclusions Opioid administration within 24 hours before cardiac arrest per se was not associated with adverse outcomes. However, administration of opioid analgesics on an as-needed basis was associated with poorer survival outcomes than regular dosing. Greater attention should be paid to patients who receive as-needed opioid administration in the general ward.