Targeting Alcohol-Opioid Co-Use Among Young Adults Using a Novel MHealth Intervention

Inclusion Criteria: 1. Ages 18 to 25 years, inclusive 2. Self-report interest in reducing their alcohol-opioid co-use - outside a research study, people who do not wish to change their co-use are unlikely to download and use an mHealth app designed to reduce co-use. It is important to recruit participants who most closely resemble the intended users of the eventual mHealth intervention. This is defined as reporting any alcohol-opioid co-use goal (i.e., not selecting "No goal" in response to the alcohol-opioid co-use goal question at the screening visit). 3. Self-report engaging in simultaneous alcohol-opioid co-use (i.e., use of both substances within two hours) ≥ 1 day/week on average in the past 28 days (i.e., at least 4 co-use events in the past 28 days). This requirement will ensure that we observe sufficient use episodes where the pharmacological effects of alcohol and opioids overlap to evaluate project aims. 4. Able to understand written and oral instructions in English, communicate understanding of the consent form, and provide written informed consent. 5. Complete all assessments required at screening. 6. Agree to the schedule of visits, verbally acknowledge that he/she/they will be able to attend each scheduled visit, participate in phone visits and that he/she/they does not have any already scheduled events or a job that may substantially interfere with study participation. 7. Own a smartphone with data plan. Almost all participants (98%) in our preliminary work owned a smartphone with data plan. 8. Currently reside in the United States of America. Exclusion Criteria: 1. Pregnant or nursing 2. Current suicidality 3. History of psychosis