Background Pharmacists have limited knowledge about adverse drug reactions (ADRs) in Saudi Arabia.Objective The aim of this study was to assess the impact of educational intervention on the knowledge of hospital pharmacists about ADRs. Methods This was a 3-month randomized controlled trial conducted in Saudi Arabia between January 2018 and March 2018. Participants in both groups were required to complete an online questionnaire at baseline and at 12-week follow-up. Participants in the intervention group received a structured information sheet about ADRs 2 weeks after the first assessment. The main outcome measure was difference in mean knowledge score about ADRs. Main outcome measure Difference in mean knowledge score about ADRs. Results A total of 46 participants were included in the study. At the 12-week follow-up, there was a significant improvement in the mean knowledge score (± standard deviation) of intervention participants from 7.67 (± 2.1) at baseline to 11.22 (± 0.4) (95% CI −4.5 to −2.5; p < 0.0001). The mean knowledge score of control participants remained unchanged at 6.71 (± 2.3) during both baseline and follow-up assessments. Conclusion ADR-specific education was associated with a significant improvement in the knowledge and understanding of pharmacists about ADRs and their methods of reporting.