Background: People in homelessness have an increased risk of substance use disorders (SUDs) and poor health outcomes. This cohort study aimed to investigate the association between homelessness and mortality in people with SUDs, adjusting for age, sex, narcotic use, intravenous drug use and inpatient care for SUDs.

Methods: Data from the Swedish National Addiction Care Quality Register in the Stockholm region were used to analyse mortality risk in people with SUDs (n=8397), including 637 in homelessness, 1135 in precarious housing and 6625 in stable housing, at baseline. HRs and CIs were calculated using Cox regression.

Results: Mortality was increased for people in homelessness (HR 2.30; 95% CI 1.70 to 3.12) and precarious housing (HR 1.23; 95% CI 0.86 to 1.75) compared with those in stable housing. The association between homelessness and mortality decreased (HR 1.27; 95% CI 0.91 to 1.78) after adjusting for narcotic use (HR 1.28; 95% CI 1.00 to 1.63), intravenous drug use (HR 1.98; 95% CI 1.52 to 2.58) and inpatient care for SUDs (HR 1.96; 95% CI 1.57 to 2.45). Standardised mortality ratios (SMRs) showed that mortality among people in homelessness with SUDs was 13.6 times higher than the general population (SMR=13.6; 95% CI 10.2 to 17.9), and 3.7 times higher in people in stable housing with SUDs (SMR=3.7; 95% CI 3.2 to 4.1).

Conclusion: Homelessness increased mortality, but the risk decreased after adjusting for narcotic use, intravenous drug use and inpatient care for SUDs. Interventions are needed to reduce excess mortality among people in homelessness with SUDs.