OBJECTIVES: To identify the determinant factors of the administrative pathway to access medicines in the Brazilian public health system. METHODS: Case-control study produced in a city in the Middle West region of Brazil. Were included 168 users in the case group, who were requesting medicines through administrative pathway in the Health Department. The control group had 435 users from Basic Health Units. The data were collected from March to July 2014 by face to face interview. The independent variables were: users’ economic and demographic characteristics, health-care characteristics, pharmaceutical care characteristics and health care conditions. The outcome variable was the administrative demand for medicines. The data were analyzed by multivariate logistic regression. RESULTS: In the economic and demographic characteristics, were significant: age (0-9 years, p=0.035; 60 and over, p˂0.001), gender (male, p=0.002), skin color (white, p=0.005) and social stratum (AB, p=0.004). In the health-care characteristics, were significant:  appointment in the public health system (rarely/never, p=0.016), information to prescriber when wasn’t possible to access medicine (all/often, p˂0.001), refusal to treatment caused by missing prescription from the public sector (all/often, p=0.009), understanding information about medicines guidance (rarely/never, p=0.013) and recommendation from public health services to people with financial resources (yes, p=0.001). In the characteristics of pharmaceutical care, were significant: medicines’ availability (excellent/good, p=0.022), treatment break due to the unavailability of medicine (all/often, p=0.007) and agreement with the rules (half the time, p=0.001). In the health care conditions, were significant: belief about the right to receive any medicine (yes, p=0.010), coverage by private health insurance (yes, p=0.012), acquisition of medicine in the private sector (all/often, p=0.025; few/never, p=0.004) and outcomes with medicines (4th quartile, p˂0.001). CONCLUSIONS: The occurrence of demands for medicines by administrative pathways is inside of a multifactorial context, including the pharmaceutical care' and health-care' characteristics, health care conditions and the users’ economic and demographic characteristics.