The article comprises a narrative review of the scientific literature, aiming to identify and discuss the contexts of vulnerability and social exclusion faced by users of crack cocaine and other substances who live on the sidelines of society in the Brazilian and international context. The paper summarizes insights from different theoretical frameworks, focusing on an integrated perspective of substance use and abuse, with an emphasis on the use of crack and its inter-relationships with social vulnerability, marginalization, social exclusion and deviation. In a first step, broad aspects of qualitative research on drugs are outlined. The subsequent section highlights issues associated with exclusion and social vulnerability of crack users, followed by an assessment of the main associations mentioned in the literature on drug use and criminal involvement. Finally, the concept of "sidelines of society" is discussed, as exemplified by situations and events experienced by users of crack and other substances, as mentioned in the literature.