The comorbidity of psychiatric disorders and drug use is a well-documented and widespread problem. In particular, substance abuse in individuals with schizophrenia shows a high degree of comorbidity, as does substance use disorder (SUD) in populations suffering from mood disorders as indicated by a lifetime prevalence of over 50% for individuals with BD. 

The patterns of comorbidity of SUDs, SS, and BD among homeless populations are much less well understood; however, it is well reported that there is a disproportionately high rate of psychiatric disorders among homeless that includes drug and alcohol use disorders. Schizophrenia for example was found in one-quarter of homeless individuals, and mood disorders were documented in one-third of homeless individuals. Symptoms of schizophrenia and psychosis has been found both in Canadian and Australian homeless populations, and affective disorders were found to be quite prevalent as well (Toro et al., 1999), with relatively stable rates across different homeless samples. Within a Canadian sample, hypomanic symptoms were also common.

 Across homeless populations, significant rates of any substance use have been reported, in particular cocaine and alcohol. Although the comorbidity of mental disorder and substance use is well documented, relatively little is understood about the potential relationship between specific substances, and specific disorders such as schizophrenia and bipolar disorder. In order to understand the relationship between substance use and mental illness, it is important to consider the role environmental and psychosocial factors play. Additionally, by studying a homeless population whose environment is uniformly characterized by an adverse psychosocial environment provides the means to examine these factors. As such, the purpose of the present study is to explore the pattern of substance use and schizophrenia spectrum (SS) and bipolar disorders (BD) in an urban homeless population.