Serious mental illnesses disrupt people’s ability to carry out essential aspects of daily life, such as self care and household management.  Mental illnesses may also prevent people from forming and maintaining stable relationships or cause people to misinterpret others’ guidance and react irrationally.  This often results in pushing away caregivers, family, and friends who may be the force keeping that person from becoming homeless.  As a result of these factors and the stresses of living with a mental disorder, people with mentally illnesses are much more likely to become homeless than the general population (Library Index, 2009).  A study of people with serious mental illnesses seen by California’s public mental health system found that 15% were homeless at least once in a one-year period (Folsom et al., 2005).  Patients with schizophrenia or bipolar disorder are particularly vulnerable.

In many situations, however, substance abuse is a result of homelessness rather than a cause. People who are homeless often turn to drugs and alcohol to cope with their situations. They use substances in an attempt to attain temporary relief from their problems. In reality, however, substance dependence only exacerbates their problems and decreases their ability to achieve employment stability and get off the streets. Additionally, some people may view drug and alcohol use as necessary to be accepted among the homeless community