Andresen discussed vulnerability as an analytical category in childhood studies and reflected on how the concept could be linked to structural, systemic and individual factors. This article starts by asking what vulnerability is and by examining its relation to agency. It suggests conceptualising agency as a dynamic experience rather than as a static condition, based on the exploration of narrative interviews with adolescent drug users (aged 16-21) in treatment. These narratives retrospectively follow the trajectories of attention-deficit/hyperactivity diagnosis and subsequent drug treatment that later developed into habitual drug use in adolescence. Our data show how drug use can shape vulnerable conditions yet also create new connections with given environments, becoming a source of agency for child and adolescent drug users. Along with the empirical findings, we reflect on the analytical potentials of Actor-Network-Theory.