Background: Bipolar disorder (BD) is a chronic psychiatric condition characterized by recurrent episodes of mania, hypomania, and depression, often resulting in significant impairment in personal, social, and occupational functioning.The study aimed to evaluate the prevalence, severity, and preventability of adverse drug reactions (ADRs) in patients diagnosed with Bipolar Disorder (BD) receiving pharmacological treatment.Material and Methods: This was a prospective observational study conducted in the Psychiatry Outpatient Department (OPD) of a tertiary care hospital. A total of 80 patients diagnosed with BD, as per DSM-5 criteria, were enrolled. Patients were followed up for six months to monitor ADRs associated with psychotropic medications. ADRs were assessed using standardized scales, including the WHO-Uppsala Monitoring Centre (WHO-UMC) causality assessment system, Naranjo’s ADR Probability Scale, Hartwig and Siegel Severity Scale, and the Modified Schumock and Thornton Preventability Scale. Statistical analysis was performed using SPSS Version 21.0, with a p-value < 0.05 considered statistically significant.Results: Among the 80 patients, 42 (52.50%) were male, and 38 (47.50%) were female. The most commonly prescribed medications were Lithium (37.50%) and Valproate (31.25%). A total of 80 ADRs were reported, with gastrointestinal (31.25%), neurological (25.00%), and metabolic (22.50%) ADRs being the most common. Causality assessment classified ADRs as probable (37.50%), possible (31.25%), certain (18.75%), and unlikely (12.50%). Most ADRs were mild (50.00%) or moderate (37.50%), with only 12.50% categorized as severe. Preventability analysis revealed that 25.00% of ADRs were definitely preventable, 43.75% were probably preventable, and 31.25% were not preventable.Conclusion: The study highlights the high prevalence of ADRs in BD patients, particularly those on mood stabilizers and antipsychotics. While most ADRs were mild to moderate, their impact on adherence underscores the need for regular monitoring, patient education, and individualized treatment strategies to optimize safety and efficacy.