Correlation between the use of ‘over-the-counter’ medicines and adherence in elderly patients on multiple medications

Background Medication adherence is a multifaceted issue that is influenced by various factors. One factor may be the concurrent use of over-the-counter (OTC) medicines. The use of OTC medicine has been reported as common amongst elderly patients. Objective To determine if a correlation exists between the use of OTC medicines and adherence to prescribed medications in elderly patients. Setting Non-institutionalised elderly patients in Denmark. Methods Elderly unassisted patients aged ≥65 prescribed five or more prescription drugs were included in the study. Information on the use of concurrent OTC medications (herbal medicines, dietary supplements, or non-prescribed drugs) was elicited during home visit interviews. Prescription drug adherence was determined by pill counts. A patient was categorised as non-adherent if the mean adherence rate for all drugs consumed was <80 %. Different sensitivity analyses were made where adherence was defined different. Main outcome measure Medication adherence based on pill-count. Results A total of 253 participants included 72 % who used OTC medicines and 11 % who did not adhere to their prescriptions. Users of OTC medicines, however, were significantly more likely to be adherent than were non-users (odds ratio 0.41; 95 % confidence interval 0.18–0.91). Sensitivity analyses where adherence was defined different show no relationship between adherence and use of OTC medicine. Furthermore, separate analyses of herbal medicines, dietary supplements, or non-prescribed drugs did not correlate with adherence to prescriptions. Conclusion Amongst elderly patients on multiple medications a positive relationship was found between the overall use of OTC medicines and adherence to prescription drugs, in contrast to none when adherence were defined different or herbal medicines, dietary supplements, or non-prescribed drugs were analysed separately.