AimsFrailty is a complex geriatric syndrome resulting in decreased physiological reserves. Frailty and polypharmacy are common in older adults and the focus of extensive studies, although little is known about the impact they may have on each other. This is the first systematic review analysing the available evidence on the relationship between frailty and polypharmacy in older adults. MethodsSystematic review of quantitative studies. A comprehensive literature search for publications in English or Spanish was performed on MEDLINE, CINAHL, the Cochrane Database and PsycINFO in September 2017 without applying restrictions on the date of publication. Studies reporting any relationship between frailty and polypharmacy in older adults were considered. ResultsA total of 25 publications were included, all of them observational studies. Evaluation of Fried's frailty criteria was the most common approach, followed by the Edmonton Frail Scale and FRAIL scale. Sixteen of 18 cross-sectional analyses and five of seven longitudinal analyses demonstrated a significant association between an increased number of medications and frailty. The causal relationship is unclear and appears to be bidirectional. Our analysis of published data suggests that polypharmacy could be a major contributor to the development of frailty. ConclusionsA reduction of polypharmacy could be a cautious strategy to prevent and manage frailty. Further research is needed to confirm the possible benefits of reducing polypharmacy in the development, reversion or delay of frailty.