Background. We evaluated adherence to medication usage by health care professionals to estimate the expected upper limit of adherence among the general population. Methods. In a self-administered survey, physicians and nurses were asked about their use of prescribed medications for acute and chronic illnesses. The settings were a teaching hospital, employee health service, medical college, and educational conferences. Results. Among 435 respondents, 301 physicians and nurses had medications prescribed for acute and/or chronic illnesses within 2 years of the survey. Of 610 prescribed medications, ≥80% were taken as prescribed, with a 77% compliance rate for short-term medications and 84% for long-term medications. Older age was associated with better adherence, whereas a greater number of doses per day was associated with poorer adherence. Conclusions. Approximately 80% of respondents reported properly taking prescription medications ≥80% of the time. Given the nature of the study population, it is unlikely that a nonclinical trial population will consistently achieve better adherence without specific interventions.