Background: Adverse drug reactions (ADRs) are common causes of mortality and morbidity globally. This study was aimed to know the pattern of ADRs and to assess its causality, severity and preventability in a sub-metropolitan city reported by community pharmacist. Methods: A cross-sectional community-based study was conducted among 200 patients in Dharan, a sub-metropolitan city in Eastern Nepal. Fifteen community retail pharmacies representing various part of the city were selected for the study. The pharmacists from the selected pharmacies were provided one-day training on pharmacovigilance and ADR reporting prior to the study. A self-designed ADR reporting form was distributed to the pharmacists to collect the sociodemographic details and suspected ADRs, the causality, severity and preventability assessment of the ADRs were conducted. The descriptive statistics were used to analyze the data using Microsoft Excel 2010. Results: A total of 332 ADRs were observed in 200 patients out of which majority were male (53.5%) and aged 18-25 years (29%). The most common ADR was nausea and vomiting (27.7%) followed by abdominal discomfort (19.3%). Antibiotics (28%) were responsible for most of the ADRs followed by non-steroidal anti-inflammatory drugs (25.5%). Diclofenac (12%) was the most common drug responsible for the ADRs followed by Cefixime (11%) and Amoxicillin (9.5%). On causality assessment, most of the ADRs were “possible” (72.5%). All ADRs were “mild” on severity assessment and “possibly-preventable” on preventability assessment respectively. Conclusions: The most common ADR was nausea and vomiting. Diclofenac was the most common drug class causing ADRs. Strategies targeting appropriate and cautious use of this class of drugs among the patients may benefit in reducing the number of ADRs. Strengthening of pharmacovigilance program involving community pharmacists might improve safe use of medicines in the community.