Importance: Patients treated in emergency departments (EDs) for opioid overdose often need drug treatment yet are rarely linked to services after discharge. Emergency department-based peer support is a promising approach for promoting treatment linkage, but evidence of its effectiveness is lacking.

Question: Is implementation of an emergency department (ED)–based peer recovery support program for opioid overdose associated with improvements in initiation of medication for opioid use disorder (MOUD)?

Findings: In this cohort study of 12 046 patients treated for nonfatal opioid overdose, those treated in EDs that implemented peer support were significantly more likely to initiate MOUD than patients treated in comparison EDs. The outcome varied across EDs and by time since peer support implementation.

Meaning: The findings suggest that ED-based peer recovery support is associated with increased post-discharge MOUD receipt, but outcomes likely depend on additional factors such as program characteristics and availability of other substance use disorder services.