Effect of different formats for information on side effects regarding medicine users’ understanding: A randomized controlled trial

•Controlled trial evaluating the understanding of side effects.•Evaluation of the most used formats for communication.•Information on side effects is not adequately understood.•Communication to the patient is flawed.•New formats for communicating side effects need to be explored. The objective of this randomized controlled trial was to evaluate the efficacy of presenting information on the risks of side effects from a medicine, presented in different formats. A randomized, parallel-group, single-center controlled trial was conducted among adult users of a training pharmacy. The information was categorized into the following groups: verbal descriptors+percentage range, percentage range and absolute percentage. The main outcomes were gist understanding and verbatim understanding, classified either as adequate or inadequate. The analyses were performed using ANOVA and Pearson’s chi-square test. A total of 393 participants were recruited from June to October 2015. Adequate levels of gist understanding and verbatim understanding were respectively 65.6% and 53.9% for the verbal descriptors+percentage range (n=128), 63.4% and 44.3% for percentage range (n=131), and 62.3% and 48.5% for absolute percentage (n=131), with no statistically significant difference between the groups (p=0.852 and p=0.299, respectively). The understanding of the information was similar in all three formats, but the percentages of adequate understanding were low. The percentage of inadequate understanding demonstrated in this study indicates that alternative formats for reporting adverse reactions need to be evaluated.