© 2017 Informa UK Limited, trading as Taylor & Francis Group Objective: The current study aimed to investigate the relationship between support provided from friends, family or broader network connections and Keyes' (2007) conceptualisation of complete mental health. Method: Participants were 1815 individuals (70% male) who entered residential substance abuse treatment provided by The Salvation Army. Questionnaires were completed by participants at their intake assessment to treatment, and 188 participants provided complete responses to a phone interview at 3-months post-discharge. Results: Changes in general support provided from friends and informal social connectedness were the strongest social variable predictors of complete mental health at 3-month follow-up. Mediation analyses indicated friends' support for abstinence had no effect on complete mental health and general social support had a direct effect on complete mental health. The relationship between informal social connectedness and complete mental health was partially mediated by alcohol use severity. Conclusions: The current findings indicate informal social connectedness and general support provided by friends is most related to one’s complete mental health in a drug and alcohol misuse context. These findings indicate supporting wider social connection (e.g. neighbours, workmates) could be a target in substance misuse treatment and aftercare.