The root causes of the opioid epidemic are complex, but inappropriate prescribing of opioids (which includes both prescribing opioids in situations where they are not indicated as well as excessive prescribing for appropriate indications) is a major contributor. Prior studies of outpatient antibiotic prescribing have shown that rates of inappropriate prescribing rise toward the end of clinicians' clinic sessions. This cross-sectional study used data from 5603 primary care physicians for acute painful conditions to analyze whether a similar relationship exists for opioid prescribing. Investigators found that the likelihood of opioid prescribing rose considerably as the workday progressed; clinicians were also more likely to prescribe opioids if their appointments were running late. In contrast, prescriptions for nonopioid therapies did not change in relation to appointment time. Although the magnitude of these effects was smaller than the variation in opioid prescribing rates between physicians found in other studies, these findings confirm that production pressure and decision fatigue contribute to inappropriate prescribing and should be addressed in quality improvement efforts to reduce opioid use.