This study aimed to describe the prevalence of access to medicines in the Brazilian Unified National Health System and associated factors among patients that received prescriptions in the public system. The study analyzed data from the National Household Sample Survey (2008). The sample consisted of individuals with prescriptions written in the National Health System in the two weeks prior to the interview (n = 19,427). The dependent variable was access to all the prescribed medicines inside the system itself. Slightly fewer than half of the sample with prescriptions received the medicines in the public health system; the proportions were higher in the South of Brazil, among black patients, those with less schooling and lower income, and those registered in the Family Health Strategy. When analyzing prescriptions written by the private sector, access to all the prescribed drugs was associated with higher income, higher education, and white skin color. The results emphasize the need for policies to decrease inequalities in access to medicines in Brazil.