The reported rates of substance use are higher among persons who experience serious mental illnesses (SMIs) than adults in the general population [1–7], and the use of drugs or alcohol is known to worsen the course of many major mental health conditions [7–17]. To date, epidemiological studies have procured general estimates of substance use among persons with SMIs [1–8], and have documented that substance use disorders (SUDs) are significantly comorbid with schizophrenia-spectrum, bipolar, and depressive disorders [1–8]. Evidence from community-based and clinical investigations also reports a high prevalence of comorbid SUDs among persons who are affected by these conditions [9–35], and that the use of drugs or alcohol by individuals with SMIs can substantially impede their recovery [9–19, 27, 31–35]. Indeed, considerable work has examined substance abuse and SMI [1–35], yet few longitudinal investigations have studied drug and alcohol use heterogeneity across the diverse population of individuals with SMIs.
