Addiction in its many forms can be both a cause and a result of homelessness. These behaviors may emerge as coping mechanisms, but often make it harder for people to return to housing. Studies have shown that homeless populations are highly vulnerable to addiction, be it substance use or other behaviors such as problem gambling, with that vulnerability increasing for chronically homeless populations. A complicating element of this relationship is the interaction between substance abuse and social support: as the social circle and support network shrink in response to substance use, vulnerability to homelessness rises. Substance abuse therefore plays a critical role in the breakdown of social bonds as well as institutional relationships, which in turn limits access to crisis housing.

Additionally, substance use can render social and economic obligations such as employment more challenging, and act as a barrier to housing services with sobriety requirements. Youth seem to be particularly vulnerable to using substances to cope with the harsh realities of life on the street. Many people experiencing homelessness who struggle with addiction exhibit high rates of comorbidity with antisocial personality disorder, post-traumatic stress disorder, bipolar disorder, and other psychiatric disorders. This is especially true for problem gamblers, who may gamble as one of a constellation of impulsive and risk-taking behaviors.