The goal of this clinical trial is to evaluate whether a smartphone app-based ecological momentary intervention called Mindful Journey, which teaches mindfulness skills, can support adults in recovery from both opioid use disorder and chronic pain. The primary objective of this pilot study is to assess the feasibility and acceptability of Mindful Journey in this population.

There is a paucity of interventions for co-occurring opioid use disorder and chronic pain. Difficulty with emotion regulation is a key shared vulnerability factor underlying both conditions. Mindfulness-Based Interventions (MBIs) are a promising intervention approach, as they target core skills that can improve emotion regulation. However, research on MBIs for co-morbid opioid use disorder and chronic pain is limited. Existing MBIs are also limited by not providing adequate support "in the moment" when individuals are in high-risk situations. A responsive, momentary MBI for co-occurring opioid use disorder and chronic pain may be highly promising, but has yet to be established. In the present study, we will be evaluating a smartphone app-based ecological momentary intervention, called Mindful Journey, for individuals with opioid use disorder and chronic pain. The core feature of the app is training in mindful acceptance and savoring skills via momentary "just-in-time" delivery of brief video-based exercises based upon ecological momentary assessments.

Inclusion Criteria:

• 18 years of age or older
• fluent in English
• enrollment in medication-assisted treatment for opioid use disorder
• report at least bothersome chronic pain, as indicated by Graded Chronic Pain Scale-Revised
• has a smartphone.

Exclusion Criteria:

• self-reporting of chronic malignant pain (e.g., cancer) or systemic inflammatory disease (e.g., rheumatoid arthritis, ankylosing spondylitis, lupus, and sarcoidosis)
• self-reporting of psychotic disorder symptoms
• participated in the previous phase of the study in which participants provided feedback to inform the development of the Mindful Journey app.

IPD will not be shared because the primary goal of this pilot study is to assess feasibility and acceptability, not to generate generalizable efficacy data suitable for secondary analyses.