There is significant interest in understanding labor market consequences of the opioid epidemic, but little is known about how opioid use affects on-the-job performance. We analyze the impact of opioid initiation on job performance using linked medical and personnel data for active-duty military members. Exploiting quasi-random assignment of patients to physicians in the emergency department, we find that military members assigned to high-intensity opioid prescribing physicians have a higher likelihood of long-term opioid use, are less likely to receive promotions, and are more likely to receive disciplinary actions and leave their jobs. Our results demonstrate productivity costs of opioid use.