Background: Adverse drug reactions (ADRs) represent a significant healthcare problem, contributing to patient morbidity and resource utilisation. This present study aimed to characterise the pattern of ADRs reported at a tertiary care hospital in Dehradun, Uttarakhand, India. Methods: A retrospective observational study was carried out by the Department of Pharmacology, Shri Guru Ram Rai Institute of Medical & Health Sciences from June 2017 to May 2018. A total of 156 completed forms were analyzed, with data on patient demographics, affected system-organ classes, implicated drug classes, and causality assessed according to the WHO-UMC criteria. Results: Males accounted for 60.3% of the 156 ADRs, while females made up 39.7%. The age distribution revealed that the majority of people were between the ages of 19 and 60 (82.1%), followed by those over 60 (12.8%), those between the ages of 13 and 18 (3.3%), and those under the age of 12 (1.8%). The gastrointestinal system was primarily affected (42.9%), followed by the cutaneous system (32.1%), the central nervous system (15.4%), and other systems. Antimicrobials were the main implicated class of drug (59.6%), followed by CNS drugs (9.6%), analgesics (8.3%). Causality assessment showed 85.3% probable/likely, 10.9% possible, and 3.8% uncertain. Conclusions: Among males of working age, antimicrobials were found to be the primary cause of adverse drug reactions (ADRs), primarily affecting the gastrointestinal and skin systems. To reduce the burden of adverse drug reactions (ADRs) and encourage safer prescribing practices, pharmacovigilance must be improved through consistent reporting and education.