The proposed study uses a randomized controlled trial to examine the extent to which the World Health Organization's SBIRT model, the ASSIST (Alcohol, Smoking, and Substance Involvement Screening Test) and its associated brief behavioral intervention, leads to reductions in substances prevalent in mental health settings: alcohol, cannabis and stimulants (i.e., cocaine and methamphetamine). The study will also examine the effect of SBIRT on improvement in psychiatric symptoms, improved quality of life and for those whose level of substance misuse indicates a need for treatment, initiation and engagement into SUD treatment services. Eligible participants will be mental health patients who report any past year use of cannabis or stimulants or at least one heavy drinking day in the past year. Mental health patients (N=750) who meet eligibility criteria will be enrolled and randomly assigned to either the SBIRT intervention condition or to a health education attention control condition. Participants will be assessed at baseline on substance use, psychiatric symptoms and quality of life. Each participant will be assessed at 3-, 6- and 12- month follow up points for alcohol and drug use, involvement in SUD treatment services, severity of psychiatric symptoms and quality of life. If successful this study will yield valuable new knowledge about the effectiveness of SBIRT in mental health treatment settings and will promote improved well being of mental health patients. Further, the study will provide evidence on the effectiveness of SBIRT for reducing illicit drug use. Results from this research will be used as the basis for broader dissemination and of SBIRT in mental health settings.