This research proposes an optimal medication purchasing policy for the Drugstore of the Department of Health of Vicuña (DESAM) for patients with chronic diseases of higher prevalence. Harris-Wilson’s economic order quantity model was used to find the optimal shopping point that minimizes storage and order costs. Of the 54 medications used for the pathologies of chronic patients, seven were analyzed, covering 71% of the demand. The results indicate that the costs of the proposed new policy for DESAM can save a little more than Ch$10 million (US$16.400).