Objective: To measure the effect of the pharmacist-led medication reconciliation service before hospital discharge on preventing potential medication errors. Methods: This behavioral interventional study took place in a public teaching hospital in Iraq between December 2022 and January 2023. It included inpatients who were taking four or more medications upon discharge from the internal medicine ward and the cardiac care unit. The researcher provided the patients with a medication reconciliation form and reconciliation form (including medication regimen and pharmacist instructions) before discharging them home. Any discrepancies between the patients’ understanding and the actual medication recommendations prescribed by the physician were identified and solved. Results: Fifty inpatients received a pharmacist-led medication reconciliation review before hospital discharge. Out of 50 patients, 44% had a clear understanding of their medications before the intervention. In contrast, 56% of the patients had at least one potential medication error before the reconciliation, which was addressed by the pharmacist's intervention. Approximately two-thirds (89.4%) of the potential medication errors were clinically significant, and 5.3% of these errors were serious. The most frequent potential error that prevented this was duplication (31.5%) (the patient was about to duplicate the same medication from different manufacturers or different medications from the same pharmacological class). Conclusion: Lack of medication reconciliation can cause significant medication errors, which might be serious and cause harm to patients. This study has the potential to shape policies and practices that prioritize medication safety and optimize patient outcomes during transitions of care.