The overall purpose of the observational, investigational pilot study is to assess the clinical utility of the Affect digital health platform (the Affect® "app") as part of the Affect program of treatment for methamphetamine-primary stimulant use disorder. The study also will identify elements of the Affect app that enhance engagement of participants in the study toward the goal of improving patient outcomes, including reduction/cessation of stimulant use.

The research project is a single-group observational demonstration study to assess the clinical utility of a digital therapeutic technology (the Affect app) in terms of participant acceptance and the app's ability to enhance retention in the Affect program of services for the treatment of individuals with meth-primary stimulant use disorder (MUD). Measures of reduction and/or cessation of methamphetamine use will be assessed by saliva drug tests at least twice weekly during each participant's 8-week involvement in the program, at end of treatment, and via self-report at follow-up points at 1, 3, and 6 months after completion of the program. The app-based program will involve the same services for study participants as would occur regardless of the research, being a standard of care for MUD. The intervention phase of the study will be completed within approximately four months, with follow-ups of the final participants occurring approximately six months after the end of the intervention phase.

To be eligible to participate in the study, prospective participants must:

1. Be 18 years of age or older;
2. Have methamphetamine use disorder (MUD) or documented high-risk methamphetamine use history, confirmed by DSM-5 criteria for stimulant use disorder, methamphetamine type;
3. Have stated interest in reducing and/or stopping methamphetamine use;
4. Have and be able to use a smartphone and agree to download and use the Affect app as part of treatment and study-related procedures;
5. Have a health insurance plan (or Medicaid) to ensure that participants have access to medical care if needed;
6. Be English speaking and have reading capacity sufficient to understand explanations of study procedures and the informed consent to participate;
7. Be a California resident with a mailing address or P.O. Box
8. Be able to freely give informed consent and be willing to electronically sign the digital informed consent to participate in the study;
9. Be willing to comply with study procedures, including use of the Affect app consistent with the study protocol and therapeutic activities.

III.6 EXCLUSION CRITERIA

Individuals will be precluded from enrolling in the study if they endorse (or if there is documentation of) any of following conditions. Already enrolled participants will be withdrawn from study participation upon emergence of any excluded condition (except pregnancy):

1. Serious medical diagnoses (e.g., seizure, stroke, heart disease);
2. Serious mental illness (e.g., schizophrenia, bipolar, active suicidality);
3. Moderate- to severe-level opioid use disorder or alcohol use disorder;
4. Pregnancy;
5. Have been in a prior study of pharmacological or behavioral treatment for MUD within 6 months of study consent;
6. Be concurrently receiving other behavioral or pharmacological services for treatment of MUD;
7. Have pending legal action or other situation that could inhibit consistent participation in the study or in study activities.

No participant data will be shared.