Objective: This study aimed to investigate adverse drug reactions (ADRs) associated with Oseltamivir in the presence of various co-morbidities. The objective was to analyze prescription patterns, administration rationale, and ADR prevalence among patients receiving Oseltamivir for therapeutic or preventative purposes. Material and Methods: The study, conducted over six months at St. Philomena’s Hospital in Bengaluru, involved patients of all ages and genders. Ethical approval secured, the research gathered data from diverse sources for 140 patients. Naranjo’s scale was employed for causation, severity, and preventability assessments of Oseltamivir-related ADRs. Descriptive statistics were utilized to compare ADR frequencies between patients using Oseltamivir for prevention and those for therapeutic purposes. Results: The study revealed a 3.57% incidence of Oseltamivir-related ADRs, with co-morbidities contributing to 2.8% of cases, predominantly associated with hypertension. The research shed light on the importance of monitoring ADRs, particularly in the context of co-morbidities during Oseltamivir treatment. Conclusion: This research underscores the importance of monitoring ADRs in the context of co-morbidities during Oseltamivir treatment. The prevalence of hypertension as the most common co-morbidity highlights the need for careful prescription practices, especially for individuals with underlying medical conditions. These findings provide valuable insights into optimizing Oseltamivir usage in diverse patient populations.