Associated Factors and Causes of Chronic Disease Medication Oversupply

Although medication oversupply results in waste of medications, triggers of medication oversupply remain unclear. This nationwide retrospective cohort study aimed to identify associated factors and causes of chronic disease medication oversupply in Japan by quantitative and qualitative analyses. Data of financial year 2019 from a large insurance claims database were used. Excess days, which represent medication oversupply in days, were calculated for each of the major five classes of chronic disease medications. For each class, the two cohorts were formed, consisting of individuals aged ≥55 years with either excessive oversupply or normal supply according to excess days. Oversupply-associated factors were subjected to quantitative analyses using logistic regression models, which included excessive oversupply vs. normal supply as an outcome variable. A qualitative analysis to identify causes of oversupply was performed by reviewing the medication history of 50 individuals randomly selected from each excessive oversupply cohort, and causes were classified into seven categories. Oversupply-associated factors in all classes were greater frequency of early supply (≥6 vs. <3 times/10 supplies, odds ratio (OR) 5-9 for all classes), inpatient prescription (included vs. not included, OR 3-5), and higher number of concomitant ingredients (≥16 vs. 1-5 ingredients, OR 3-5). The most common category of causes for oversupply in all classes was the "early supply of medications prescribed by a single facility." The factors and causes of oversupply might reflect the unique features, rules, and customs of Japan's healthcare system. This finding might help in developing measures for reducing medication oversupply.