A common problem observed in patient safety is the lack of accurate and complete information about medications in regular use during transfers of care between different health facilities. In view of this, medication reconciliation is postulated as a barrier to reducing medication discrepancies and consequently medication errors. This project aims to evaluate the implementation of safe clinical practices conducted by clinical pharmacists. To this end, we will conduct a standardized process to obtain the best possible medication history (BPMH); assessment of the patient's level of understanding of pre-admission therapy; quantification, classification and analysis of discrepancies of unintentional drugs at hospital admission; effect of interventions conducted by clinical pharmacists and impact on patient safety. This prospective, pilot, descriptive, interventional and single-center study will be carried out in the Clinical Pharmacy Department of a large hospital in the state of São Paulo. In order to standardize the process of data collection and reconciliation of prescription drugs, the interview with the patient will be carried out using an adapted and modified form. After collecting information in the structured interview, clinical pharmacists will identify, analyze and classify possible discrepancies. All unintentional discrepancies found without any clinical justification will be considered medication errors. Finally, the degree of impact of each drug discrepancy will be defined as: clinically insignificant; clinically significant; serious and life-threatening.