The number of older adults in the world is expanding rapidly as a consequence of increased quality of life and technological advances. 1,2 This demographic transition is increasing the prevalence of chronic-degenerative diseases. One of the consequences is higher consumption of medicines, which implies a great challenge for the healthcare system. 3 Given that use of several drugs is needed to treat the multimorbidity commonly seen in older adults, it can be expected that the prevalence of polypharmacy among older adults and the risk of drug interactions will increase substantially. 4 Drug interactions are a common cause of adverse drug reactions among older adults, and these include arrhythmias, acute kidney injury and increased risk of falls. 5-7 A direct correlation between the number of medications and their interactions and the risk of adverse drug reactions has been shown. 4-7 The reasons for this are multifactorial and particularly include age-related changes in the pharmacodynamics and pharmacokinetics of drugs, reduced renal function and lower hepatic clearance. 6-8 At hospital discharge, older adults generally present changes to their drug therapy, with higher numbers of prescribed medications, which leads to higher frequency of drug interactions. 8 Thus, it is essential to know the frequency of these interactions at hospital discharge among older people and their determinants, in order to promote safer use of drugs among older adults.