Abstract Background Supervised injectable opioid treatment (SIOT) is a promising alternative for people living with opioid use disorder (OUD) who have not sufficiently benefitted from oral opioid substitution treatment. Yet, SIOT utilization remains limited in Germany. We propose that this is due to beliefs, or schemas, on SIOT among people living with OUD. Drawing from medical sociology and social psychology, this study explores the emergence and evolution of such schemas on SIOT. Methods We conducted semi-structured interviews with 34 individuals currently in or eligible for SIOT in two German outpatient treatment facilities and paralleled an inductive qualitative content analysis with the exploration of individual cases. Results The analysis revealed that peer-to-peer interaction and individuals’ practical experiences in therapy are crucial in constructing and changing idiosyncratic and shared schemas of SIOT. When facing ambiguous information, cognitive strategies like subtyping served to mitigate uncertainty. Conclusion This research has important practical implications for integrating experiential knowledge into clinical care and improve information sharing among people living with OUD. A nuanced understanding of the complex network of informal advice-seeking and -giving among people living with OUD is indispensable to adequately expand treatment modalities of proven effectiveness.