This article examines the growing awareness of drug addiction as form of mental illness in several Canadian lunatic asylums in the last half of the nineteenth century and the beginning of the twentieth. Whereas in the 1870s and 1880s, medical and reform associations formed to cure and treat addiction and inebriety, asylum evidence suggests that it was not until the turn of the century that drug habituation was considered a condition which merited admission to asylum. Prior to the turn of the century, drug use appeared in the psychological profile of asylum entrants only as an attendant condition of a more traditional form of mental illness, such as mania or melancholia. Asylum physicians, seeking traditional categories, and utilizing subjective classification methods, generally would not consider addiction to be a distinct mental illness. At the end of the century, shifts in diagnostic convention and the official endorsement of those shifts signalled a change that was taking place in the asylum. The impact of drug addiction on the psychological profile of a patient was attracting more attention in the asylum. Subsequently drug addiction joined other earlier causes of mental illness, such as masturbation, and also began to be recognized as a mental condition worthy of treatment at the public asylum. Its status as mental disease proper, however, remained a point of debate.