OBJECTIVES: To identify the prevalence of potential drug-drug interactions (DDIs) in the prescriptions dispensed in a tertiary-care hospital of Lahore, Punjab, Pakistan. METHODS: A retrospective analysis of 600 prescriptions fulfilling inclusion criteria was conducted in a tertiary-care hospital, from November 2015 to March 2016. The collected data contain demographics, medications, diagnosis, co-morbid conditions and length of hospital stay. Medscape database was used for the therapeutic and/or pharmacological classification of prescribed drugs. The prescriptions were analyzed for potential DDIs by using the drug interaction checker. The DDIs were also classified on severity basis as major, moderate and minor. For statistical analysis SPSS version 21.0 was used. RESULTS: Overall prevalence of DDIs was 71.3%. Out of 600 sample size, approximately 428 prescriptions have potential DDIs. Average of 3 DDIs was found in each prescription. The prevalence rate of major interactions were 14.3%, moderate 50.3% and minor were 28.7%. Maximum number of major interaction in a prescription was 4, moderate 9 and minor was 6. Highest percentage of interactions was found in the prescriptions of cardiology ward (53.1%). The DDIs were significantly associated with increased number of drugs prescribed (P-value 0.000). CONCLUSIONS: Potential DDIs occurrence was significant. Patients admitted to cardiology ward and those with large number of prescribed drugs need to be monitored more closely.