BackgroundThe patient package inserts (PPIs), which contain the necessary information about medications intended for patients, need to be expressed in a clear language comprehensible to everyone.ObjectiveThis study aimed to evaluate the readability and understandability of the drug package inserts for the inexpert people.MethodsThe readability of the 158 PPIs of the 33 drugs, registered and manufactured in Iran, was calculated. The main criterion for selecting PPIs to include in this study was of those top-selling drugs during the year 2015 according to the Social Security Organization in Iran. The PPIs were collected from the pharmacies of the three major cities, namely, Tabriz, Ardabil and Meshgin Shahr. Then, using the Flesch–Dayani readability (FDR) tool adjusted for the Persian language, the average number of the words and syllables was counted to calculate and grade the readability score of the selected PPIs.ResultsThis study showed that the average FDR readability score for all the 33 drugs is 52.52, which are graded 10th–11th. Of the PPIs, 70.89% were difficult to read, and on average, the readability of the PPIs was five times difficult than the standard ones. Only 13.92% PPIs were suitable for the 5th–7th grade, and 15.19% of the package inserts ranked in the 8th–9th reading grade.ConclusionA considerable number of the PPIs in Iran have low readability level and were not suitable for the inexpert readers. Since the treatment cost is very high, people tend to use medications arbitrarily or simply use old prescriptions. This study suggests the necessity of a major improvement in the readability level of the PPIs in order to ensure the usefulness of the PPIs to the majority of the consumers.