The concept of risk, and its centrality to social life, is theoretically much discussed within late modernity. This paper examines young people's drug use and their drug transitions within a framework of risk drawing on findings from a longitudinal ethnographic study of drug use among young people in a Dublin inner-city community. Fifty-seven young people aged between 15 and 19 years, including non-users, recreational, and problematic drug users, were recruited into the study in 1998. Contact was re-established with 42 of the study's participants in 2001. Individual interviews and focus group discussions, supported by prolonged participation within the study site, were the primary methods of data collection. Drawing on the young people's situated accounts of their drug-taking events, routines, and practices across time, the findings highlight the complex social negotiations involved in the construction of drug journeys. Analyses of change in drug use behaviour over the study period demonstrate that drug transitions unfold alongside dynamic and changing perceptions of safety and risk. Responses to "risk" within youth drug scenes were contextually shaped, open to situational revision over time, and, in many instances, drug taking was habitual, not calculated. Put differently, young people "script" risk as they gain experience in the world. The type of calculus involved in the making of drug journeys is fluid and relational, socially contingent rather than static, and subject, at times, to constrained agency linked to social and economic marginalization. It is argued that models of risk that rely on individualistic and rationalistic assumptions struggle to accommodate the fluidity and contradiction that characterizes much drug use. Implications for strategies and initiatives aimed at reducing drug-related harm are discussed.