BACKGROUND: People bereaved by drug overdose experience a "special grief" that includes guilt, shame, and blame for their loved one's death, which often compounds suffering and interferes with help-seeking. This population is vulnerable to poor health outcomes including prolonged grief disorder, risky substance use, and suicidal thoughts and behaviors. Peer grief support may reduce risks in people bereaved by overdose by buffering grievers from the negative effects of increased stigma and isolation. Peer Support Community Partners has developed the RIVER peer grief support model for bereavement. The model has been implemented successfully in the community and for drug overdose bereavement, but has not yet been rigorously tested. METHODS: The current study is a two-phased project that aims to test whether the RIVER peer grief support approach improves health outcomes in those grieving drug overdose deaths. In the first phase, we will prepare for and conduct a pilot test of the RIVER peer grief support approach. We will also assess an innovative mechanism for engaging grievers through Medical Examiners Offices (MEOs). In the second phase, we will compare enhanced usual care (EUC) to EUC plus RIVER peer grief support (RIVER) in a randomized controlled trial. CONCLUSIONS: The study aims to build the science of overdose bereavement and provide increased support for a vulnerable population of grievers. TRIAL REGISTRATION: https//clinicaltrials.gov/study/NCT06854757.