Substance use disorders are common among persons experiencing homelessness, and research has identified social networks as important correlates of substance use in this population. Permanent supportive housing (PSH), particularly Housing First, which uses a harm reduction model not requiring substance abstinence, is a key solution for ending homelessness. However, conflicting evidence exists regarding the associations between moving into PSH and changes in substance use, and there is limited understanding of how networks may influence such changes.

Using observational, longitudinal data from 421 persons before they moved in and over their first year in PSH (collected as part of a HIV-risk study), this paper assesses substance use change (alcohol, marijuana, and illicit drugs) and associations between perceived network characteristics and individual substance use.

Substance use remained relatively stable among participants over their first year living in PSH, although illicit substance use reduced somewhat at six months compared to baseline levels (from 18.5%–14.5%) and marijuana use increased slightly at 12 months (from 26.6% at baseline to 32.9%). Substance use among social network members was consistently associated with individual-level substance use, both cross-sectionally and longitudinally. Specific network substance use characteristics, such as proximity, location met, and social support, had differential relationships with particular substance types.

These findings provide longitudinal evidence that changes within substance-using social networks are associated with subsequent changes in individual use and underscore the importance of interventions aimed at promoting positive social relationships for formerly homeless persons and improving PSH’s social environments.