Polypharmacy and functional decline in activities of daily living in older rehabilitation inpatients: a retrospective observational study

Polypharmacy is common in older rehabilitation inpatients and may interfere with functional recovery. However, its impact across different types of rehabilitation remains unclear. This retrospective observational study included 1,903 patients aged 65 years or above who underwent rehabilitation between April 2017 and March 2024 at a convalescent hospital in Japan. Patients were categorized by type of rehabilitation into cerebrovascular, motor disorder, and disuse syndrome groups. Functional outcomes were evaluated using the Functional Independence Measure score (FIM) and Barthel Index (BI). Polypharmacy was defined as the concurrent use of 6 or more regular prescription medications. Multiple linear regression analyses were conducted to evaluate the associations between polypharmacy and rehabilitation outcomes. Of all patients analyzed, 62.1% had polypharmacy at discharge, and 76.4% were aged 80 years or older. In the cerebrovascular disease group, polypharmacy was significantly associated with reduced FIM gain (unstandardized coefficients [β] = -3.225, p = 0.029), but was not significantly associated with BI gain. Likewise, a significant association of polypharmacy with lower FIM gain but no significant association with BI gain was observed in the disuse syndrome group. In contrast, no significant association between polypharmacy and FIM gain or BI gain was found in the motor disorder group. Age-stratified analysis revealed a stronger negative association between polypharmacy and functional recovery in patients aged 80 years and above. Furthermore, an increase in number of medications prescribed during hospitalization was independently associated with poorer FIM and BI outcomes. Polypharmacy was also associated with higher rates of using benzodiazepine receptor agonists, laxatives, and psychotropic drugs. Polypharmacy at discharge was negatively associated with functional recovery, particularly among patients with cerebrovascular disease or disuse syndrome. These findings highlight the importance of medication review and deprescribing to optimize rehabilitation outcomes in older inpatients.