Adverse drug reactions (ADRs) are an important public health problem, representing a major cause of morbidity and mortality. However, several countries have no recent studies available. Aim: to study on the incidence, causality and severity assessment of adverse drug reaction on in-patients and out-patients in a tertiary care teaching hospital. Methodology: A prospective observational study was conducted in a tertiary care hospital for six months. The study was conducted in the department of both inpatient / outpatient except psychiatric and pediatrics patients of Karuna Medical College Hospital, Kerala. This scale was developed to help standardize assessment of causality for all adverse drug reactions and based on this scale; the severity of adverse drug reactions was classified. Results: A total of 100 patient’s data was collected from Karuna Medical College Hospital, located in Palakkad, Kerala. Among the collected cases we identified 24 Adverse Drug Reactions. The most commonly observed reactions in our study was found to be Constipation (37.5%). Conclusion: we conclude that the mild reactions were highest. Predictability of the reaction were assessed and Type A predictable kind of reactions are commonly seen. Similarly, preventability assessment of ADRs was performed using modified Schumock and Thornton criteria and found that most of the ADRs were definitely preventable