Objectives: Dual diagnosis refers to co-occurring substance use and psychiatric disorders. The principal aims of this investigation were two-fold: 1) to identify aspects of patients' drug use and prior treatment histories associated with their receiving a dual diagnosis upon admission to the Donwood Institute, a residential drug treatment facility located in Toronto, Canada; 2) to track temporal trends in the rates of diagnosed comorbidities over a five-year period at this same institution.

Methods: We conducted an analysis of the intake assessment forms and hospital records of 159 patients who had been admitted to a drug treatment facility during the month of September for each of the years between 1998 and 2002 inclusive. Comparisons were made between patients who had received a psychiatric diagnosis on admission and patients who had received no such diagnosis. We then employed logistic regression analyses to explore the relationship of the variable psychiatric diagnosis on admission to other patient variables.

Results: Among the patients studied in our sample, those receiving psychotherapy or taking prescription psychotropic medication at the time of their admission as well as patients whose primary problem substance was cannabis or who had been previously admitted to the treatment facility were significantly more likely to have received a psychiatric diagnosis on admission, in spite of our finding that several patients receiving psychotherapy or taking at least one psychotropic medication did not receive a psychiatric diagnosis on admission.

Conclusions: Whilst our data indicate that psychiatric comorbidity is common among individuals in treatment for substance use disorders at the Donwood Institute, it is possible that some individuals with psychiatric illness in our sample were not diagnosed as such when presenting for treatment of their substance use difficulties. Moreover, temporal tracking of rates of dual diagnoses did not reveal a consistent increase during the period studied.