This study investigates the type and extent of changes in route of drug administration among heroin users after treatment: whether injectors move to other routes of use; whether changes in route for one drug influence routes used for other drugs; and associations between changes in route of administration and other substance use outcomes. The sample comprised 641 heroin users recruited to 54 UK treatment programmes. At intake, the main routes of heroin use were injecting (61%) and "chasing the dragon" (37%). After 1 year, 81% of those using heroin took it by the same route as at intake, while 19% reported a change, with 14% switching from injecting to chasing. Changes from injecting to chasing were associated with improvements in other substance use behaviours. Changes in route represent an important aspect of drug-taking behaviours. Interventions to prevent the change to injecting should be developed and offered to noninjectors. "Reverse transitions" (from injecting to chasing) may represent a useful intermediate treatment goal for drug injectors who cannot achieve abstinence.