OBJECTIVES: Older people are particularly vulnerable to adverse effects of prescribed drugs. PIP can be defined as the use of medicines with an unfavourable risk benefit ratio. There has been little research on the relationship between PIP and humanistic outcomes, such as functional impairment.  This study aims to measure the prevalence of PIP in an older Irish population and to investigate its association with IADL impairment.  METHODS: A retrospective cohort study of 2,051 community-dwelling participants in The Irish Longitudinal Study on Ageing (TILDA) aged ≥65 years with linked medication dispensing history from a national pharmacy claims database was carried out. Exposure to PIP in the 12 months prior to assessing functional impairment was determined using the Screening Tool for Older Persons’ Prescriptions (STOPP), the Beers’ criteria (2012) and Assessing Care of Vulnerable Elders (ACOVE) indicators relating to inappropriate medications. Logistic regression was used to determine the association between exposure to PIP and presence of any IADL impairment, adjusting for age, gender, socioeconomic status, number of repeat drug classes co-morbidity and medication adherence. RESULTS: The overall prevalence of PIP was 66.89% (n=1,372). Of these 514 (25.06%) had one instance of PIP, while 858 (41.83%) had two or more. Prevalence was highest using the STOPP criteria (57.29%), compared to prevalences of 37.64% (Beers’ criteria) and 23.5% (ACOVE indicators. Participants with ≥2 PIP indicators were significantly more likely to have an IADL impairment (adjusted OR=1.91; 95%CI=1.15-3.18) compared to no PIP. Similar associations were found for the individual measures of PIP. Age, number of repeat drug classes and co-morbidity were also significantly associated with IADL impairment. CONCLUSIONS: PIP in the elderly is highly prevalent and exposure to PIP is independently associated with increased risk of having IADL impairment. This suggests the importance of considering appropriateness when prescribing medicines in order to minimise adverse outcomes.