Research about accessibility to medicines through household surveys is very important in order to verify the reality and effectiveness of interventions done to increase the access of the population to the medications. Unfortunately, such studies, on top of being very few, have methodological problems, which mostly result from a lack of uniformity in the operational defnitions of access and the differentiation with the dimensions of accessibility. The aim of this paper is to propose setting a difference between both terms. We propose an operational defnition of access to medications as the process of verifcation of the purchase of a drug by a patient, independently from many factors that can affect this process. The term "usability of drugs" is introduced, defning it operationally as aimed at measuring the dimensions of the accessibility to the medications: physical availability, affordability, geographical accessibility, acceptability (or satisfaction).