The opioid crisis remains a significant public health emergency. Key contributors to this crisis include an increasingly toxic drug supply and inadequate health policies that rely on strategies to address opioid-related harms and underutilise primary prevention and early intervention approaches. To inform comprehensive prevention and early intervention strategies, research is needed to explore pathways involving hazardous opioid use (ie, daily opioid use that results in, and may arise from, disruptions to health, relationships, work or social functioning) and the individual, social and structural factors that shape such pathways. This qualitative study aims to address this research gap by exploring the substance use journeys of adults with lived or living experiences of hazardous opioid use who are receiving substance use treatment at a large Canadian mental health hospital.

A qualitative descriptive study informed by the life course perspective will be conducted. Data will be collected using participant-led timeline mapping in combination with semistructured interviews. Participants will include 20–30 adults who are receiving or have received substance use treatment from the hospital where the study is being conducted. Timelines and interviews will be analysed using thematic analysis. A brief demographic questionnaire will also be administered to describe characteristics of the sample.

Ethical approval was granted on 1 October 2025 by the Centre for Addiction and Mental Health Research Ethics Board (Protocol no. 2025/026). Findings will be reported through peer-reviewed publications, lay language reports and/or academic conferences on mental health and substance use health research.