Listen to your Doctor, or else!: Medication Under-use and Overuse and Long-term Health Outcomes of Danish Diabetes Patients

We use Danish diabetes registry and health insurance data to analyze the extent, consequences, and determinants of under-use and overuse of oral anti-diabetic drugs. Less than half of patients consume the appropriate amount of medication--between 90% and 110% of the amount prescribed by their doctors. The life expectancy of patients consuming the appropriate amount is 2.5 years greater than that of patients consuming less than 70% of the prescribed amount, and 3.2 years greater than that of patients consuming more than 130% of the prescribed amount, controlling for time since diagnosis, insulin dependence, comorbidities, age, gender and education. Patients consuming the appropriate amount are also less likely to be hospitalized than under- or over-users. Pharmaceutical innovation appears to have reduced medication under-use and overuse: patients using newer drugs are significantly more likely to consume the appropriate amount, controlling for socioeconomic factors, average number of pills and average daily out-of-pocket costs. Defined Daily Doses published by the World Health Organization substantially overstate the appropriate level of consumption of these medications. Patients who don’t adhere to recommended medication regimens may also disregard other physician instructions. Medication under-use and overuse could easily be monitored to identify patients at risk and enact interventions.