OBJECTIVES : Drug-Drug interaction is characterized when the desired effects of a drug are modified by the presence of other drugs. In this work, the interactions between drugs were approached and the pharmacoeconomy of waste by model were calculated. The analysis is focused on medications for Diabetes Mellitus, Arterial Hypertension and Dyslipidemia. METHODS : Adherence to the program was voluntary, so they had to submit their resources to be evaluated by the program's Pharmacists. After receiving the medical prescription, the Pharmacists guided the patients and answered their questions about the treatment, the adverse effects of the medications and the scheduled delivery of the medication. In this program the beneficiaries had an active follow-up by the Pharmacist and could easily buy and receive the medications prescribed by the coordinating care team. RESULTS : A total of 2,146 patients undergoing treatment for chronic diseases from January 2014 to September 2018 were enrolled in the program. 784 patients presented mild interactions; 3,496 had moderate interactions and 289 serious interactions. This study observed that early detection and recognition of drug interactions is vital to identify patients who are at higher risk and who could be a candidate to change drugs in order to decrease waste status. We hypothesized that the prediction of DDI was able to calculate the pharmacoeconomics of waste , but fail at the moment . CONCLUSIONS : Pharmacoeconomic studies of waste categorize costs as intangible. Adequate prescriptions, health monitoring and education are essential to reduce the risks of drug interactions. The active follow-up of the treatment through pharmaceutical assistance enables the recovery of the pharmacist’s role in eldercare, the evaluation of the risks of interactions from the moment the patient receives the medical prescription until the clinical outcome at the end of the treatment, thus decreasing drug waste.