Inclusion Criteria:  To be eligible to participate in the study, prospective participants must:  Be 18 years of age or older; Have methamphetamine use disorder (MUD), confirmed by DSM-5 criteria for stimulant use disorder, methamphetamine type, endorsing >3 DSM-5 Checklist items (see Note below*); Have stated interest in reducing and/or stopping methamphetamine use; Have and be able to use a smartphone and agree to download and use the Affect app as part of study-related procedures; Be English speaking and have reading capacity sufficient to understand explanations of study procedures and the informed consent to participate, which will be prepared at 7th-8th grade level; Have a mailing address, P.O. box, or other means of receiving packages (for biologic sample kits) as a resident of Arizona; Be able to freely give informed consent and be willing to electronically sign the digital informed consent to participate in the study;  Be willing to comply with study procedures, including use of the Affect app consistent with the study protocol and therapeutic activities.  Note: The inclusion criterion of MUD is established via the screening process involving questionnaires about meth use and the candidate's endorsement of DSM-5 criteria for MUD. We are confident in this process, given the fact that all of the participants (N=57) enrolled in our field study (Study # 1302084, IRB Tracking # 20210518, completed June 2021) tested positive for meth by the twice-weekly biologic tests during Weeks 1 and 2 of the intervention period, which confirms validity of the eligibility criterion of MUD determined by DSM-5 Checklist at screening.  Exclusion Criteria:  Individuals will be precluded from enrolling in the study if they endorse (or if there is indication of) any of the following items. Already-enrolled participants will be withdrawn from study participation upon emergence of an excluded condition (except pregnancy):  Serious medical condition (e.g., seizure, stroke, heart disease); Serious mental illness (e.g., schizophrenia, bipolar, active suicidality); Moderate- to severe-level opioid use disorder or alcohol use disorder at screening (DSM5 checklist); Currently pregnant or planning on becoming pregnant (which may indicate a need for higher level of care to ensure safety of the woman and fetus); Have been in a prior study of pharmacological or behavioral treatment for MUD within 6 months of study consent; Be concurrently receiving behavioral or pharmacological services for treatment of MUD; Have pending legal action or other situation that could inhibit consistent participation in the study or in study activities. Have any other condition that, in the opinion of the PI and the Co-Investigator (Jeff DeFlavio, M.D.), would interfere with participation in and completion of this trial or would put individuals at risk to their well-being.