Study Objectives: The United States is in the midst of an opioid epidemic. Of more than 42,000 opioid deaths in 2016, 40% were related to prescription medications. Emergency department (ED) visit prescriptions may provide the initial exposure for many patients who subsequently misuse or develop opioid use disorder (OUD). Physician prescribing patterns can vary extensively, however ED physicians are among the top 5 opioid prescribers in all medical specialties in almost all age groups. It is well documented that a larger quantity of tablets or prolonged prescription duration is associated with increased risk of chronic opioid use. Electronic health records (EHR) allow for implementation of active and passive interventions that may influence provider behavior, specifically the ability to set prescription preferences on the departmental level. We tested the hypothesis that decreasing the number of pills in our ED prescribing preference settings would decrease the duration of prescriptions and number of tablets for opioid medications prescribed by our providers.Methods: A pre-post study design was performed between 4/1/17 and 4/30/18 using all opioid prescriptions made through EPIC Corporation's 2015 ASAP EHR module in 2 EDs. Prior to the intervention, which occurred on 1/28/18, opioid prescriptions had the EHR default prescription settings, which varied in number of pills and durations. Using the CDC guidelines for opioid prescribing, all opioid entries were given defaults under 50 milligram morphine equivalents per day and supplies were only for 3-days. Opioid prescriptions, their dosages and total pills dispensed were abstracted using the institutional reporting software Qlik. Our outcome measures were rates of prescription attributes that were consistent with CDC guidelines. Chi-square and Mann Whitney test were used to determine statistical significance.Results: During the study period, there were 78,416 discharged patients, of whom 731 (0.093%) received opioid prescriptions. 503 (69%) of these prescriptions were for >3 days of therapy. Comparing the pre period to the post period there was a reduction in the median number of all opioid prescriptions per month (56 [IQR, 49.9-62.2] to 47 [IQR,[45][46][47][48][49], p ¼ 0.014). There was also a reduction in the proportion of prescriptions lasting >3 days (80% [95% CI, 76.5-83.1%] to 19.3% [95% CI, 13.2-27.1%], p<0.001), as well as a reduction in median number of pills dispensed (12 [IQR,[8][9][10][11][12][13][14][15][16] to 8 [IQR, 6-10], p<0.001).When isolating the 3 months pre and post intervention there was no difference in the median number of overall opioid prescriptions. However, there was a reduction in proportion of prescriptions lasting >3 days (70 .5% [95% CI, 62.6-77.4%] to 19.3% [95% CI, 13.2-27.1%], p<0.001), as well as the median number of pills dispensed (11 [IQR,.5] to 8 [IQR, 6-10] p<0.001).Conclusions: Modification of departmental EHR prescription preference settings can substantially alter prescribing patterns for opioid prescriptions in the ED. ...