OBJECTIVES: Diffusion rates of drugs refers to the rate of adoption for patients utilization in a given healthcare system after its incorporation. The Brazilian Public Healthcare System (SUS) supplies free universal health coverage. The Brazilian Agency for Health Technology Assessment (CONITEC) has completed 4 years; thus, the purpose of the study was to identify the main factors influencing drug diffusion rates after inclusion in the Specialized Pharmaceutical Services Component (CEAF), the high cost drug list, of SUS by CONITEC. METHODS: The study is based on the statistical analysis of variables selected in claim databases (DATASUS) of the SUS available at CEAF. The data selected included drugs with at least 3 years of incorporation into CEAF. An univariate analysis with 17 variables was performed, using data available on drugs characteristics, treated diseases, number of patients, prices, and other attributes that could affect diffusion rates. Then, an exploratory multivariate probabilistic regression probit analysis was performed to identify covariates influencing drug diffusion rates. RESULTS: Eight variables were selected in the probabilistic model as determinants of higher rates of drug diffusion into the SUS: cost of treatment, time lag between incorporation and publication of clinical guidelines, number of patients on treatment, previous treatment for the disease in SUS, innovative drug, patent, continuous use, and use associated with another drug. Two variables showed negative influence: number of competing drugs for the same disease treatment and drug price higher than the price of other drugs already in adopted in SUS. CONCLUSIONS: The exploratory multivariate analysis of data from SUS allowed to identify variables that may impact the rate of drug diffusion in the Brazilian healthcare system. The preliminary analysis performed can provide relevant information for Brazilian policymakers on budgetary impacts for SUS regarding adoption of new drugs with high prices.