The abuse of alcohol and other drugs is an important mental health issue in the adult and adolescent population. Along with other concerns, substance use can be associated with a higher vulnerability to HIV infection. This study aimed to assess the relationship between three variables in substance users:HIV perceived severity, condom use self-efficacy, and HIV vulnerability. This was a cross-sectional, quanti-qualitative study on outpatients from a Psychosocial Care Center for Alcohol and Other Drugs (CAPSad) in Brazil. Our findings indicate no significant association between HIV perceived severity and HIV vulnerability (Spearman's ρ of -0.109 and p-value of 0.507), and a marginally significant negative association between condom use self-efficacy and HIV vulnerability (Spearman's ρ of -0.302 and p-value of 0.061). In this paper, we discuss the stigma related to HIV/aids and criticize fear-based preventive interventions, recommending against them. On the other hand, we propose strategies for self-efficacy development, aiming to strengthen the autonomy of CAPSad users.