Background: Addiction Consult Services (ACS) have become an emergent clinical intervention for persons with substance use disorders (SUD) requiring hospital-based care. However, there have been few recent evaluations of the evidence for the effectiveness of ACS on SUD outcomes.Objective: We aimed to assess the effectiveness of ACS for persons with SUD on a range of SUD-related outcomes.Methods: We systematically reviewed peer-reviewed scientific literature measuring ACS outcomes. We searched 5 electronic sources (PubMed, MEDLINE, CINAHL, Cochrane, and EMBASE) from database inception through April 2021 and hand-searched article bibliographies for additional records. In addition, we considered any interventional or observational study design presenting original data and appraised study quality with the Joanna Briggs Institute checklist. Assessed outcomes included pharmacotherapy initiation in-hospital and postdischarge, retention in addiction treatment, length of hospital stay, 30-day readmissions, deaths, and patientdirected discharges. Finally, we conducted a narrative synthesis due to study design and outcome measurement heterogeneity.Results: From the initial pool of 1057 records, 26 studies (n = 12,823 participants; 60% male; mean age: 41 y) met review inclusion criteria. Most ACS provided pharmacotherapy, usually medications for opioid use disorder; add-on services varied, with some also providing psychotherapy (69%), discharge planning services (23%), and infectious disease consultation and treatment (19%). Overall, 7 studies (27%) observed positive impacts of ACS compared with control interventions on postdischarge engagement in addiction treatment and reduced addiction severity. Four studies (15%) reported no significant impacts of ACS versus control interventions on postdischarge care utilization or injection drug use frequency. The remaining 15 studies (58%) described the uptake of ACS-delivered treatments by hospital-based samples of patients with SUD but did not compare against a control condition.