Introduction: Diabetes mellitus (DM) is a serious health problem worldwide. The unhealthy lifestyles, such as smoking, lack of physical activity, high glucose/calories intake, and alcohol consumption, are thought to be the risk factors for diabetes. Uncontrolled blood glucose level will increase the risk of complications such as microvascular and neuropathy. Patientâ€™s knowledge of DM and medication administration is required to prevent the complication of diabetes. Patient advocacy can increase the patientâ€™s knowledge. Materials and Methods: The purpose of this study was to determine the influence of patient advocacy on their knowledge of medication administration and decrease in blood glucose levels. This pre-experimental one-group pretest-posttest study was conducted on 58 patients with DM. The collected data were including blood glucose level and patientâ€™s knowledge. A questionnaire was used to collect the data of patientâ€™s knowledge. Data were analyzed using paired t-test. Results: The results showed the average knowledge before advocacy was 7.07, while the average blood glucose level was 239.48 mg/dL. After patient advocacy program, average knowledge was 7.95, while the blood glucose level was 208.52 mg/dL. Discussion and Conclusion: It can be concluded that patient advocacy increases patientâ€™s knowledge of drug administration and influences the decrease in blood glucose levels.