Objective: Adolescent substance abuse is a public health concern worldwide, and its prevention is the subject of numerous programmatic efforts. Yet, little research exists on the structure of drug-related belief patterns in youth and their utility in preventive program planning. The aim of this study is to determine the structure of drug-related beliefs among 12-15-year-old students in Brazil using latent class analysis. Methods: De-identified survey data were obtained from the baseline sample (n=6,176) of a randomized controlled trial on the #Tamojunto drug use prevention program in Brazilian middle schools. Using 11 survey items assessing drug-related beliefs as indicators, four models were run and assessed for goodness-of-fit. For the best fitting model, demographic variables and substance use across latent classes were assessed. Results: Model fit statistics indicated that the best fit was a three-class solution, comprising a large Drug-Averse Beliefs class (80.9%), a smaller Permissive Beliefs class (12.7%), and an Inconsistent Beliefs class (6.4%). Respondents in the Permissive Beliefs and Inconsistent Beliefs classes reported greater past-year drug use, were slightly older and less likely to be female than those in the Drug-Averse Beliefs class. Conclusions: These results indicate that conceptualizing drug beliefs as a categorical latent variable may be useful for informing prevention. Longitudinal studies are needed to establish temporality and assess further applicability of this construct.