Aims: The research on motivations and meanings associated with drug use in prisons has received little scholarly attention. Particularly, there are few studies analysing drug use in prisons from the perspective of both prisoners and prison officers, and in the context of prisonbased drug rehabilitation. This article explores prisoners and prison staffs perceptions on why drug use occurs in prison. Methods: The data is derived from participant observation and qualitative interviews (N ¼ 35) conducted during eight months of ethnographic fieldwork in two drug rehabilitation programmes in a closed Norwegian prison. Findings: Prison staff emphasises drug addiction and prisoners troubled life trajectories when explaining in-prison drug use. Prisoners, on the other hand, explain that drug use can be (a) a way to alleviate some of the pains of imprisonment; (b) an integral part of social life in prison; (c) a route to status in the prisoner community and (d) a defiant way to subvert institutional rules and expectations. Conclusions: Prison staff tends to privilege pre-prison characteristics when explaining prisoners' drug use, whereas prisoners tend to privilege how the prison context motivates and give meaning to their drug use. Implications for penal policy and practice are discussed.