Efficacy of an EMDR App for PTSD and SUD

Inclusion Criteria: * Aged 18-years old or older * Fluent in English * Diagnosed with PTSD by the PTSD Checklist for DSM-5 (PCL-5 past month version score \>32) * Diagnosed with past-year substance use disorder other than caffeine by structured clinical interview for DSM-5 (SCID-5) * Agrees not to participate in other treatments during the study duration (e.g., mindfulness, yoga, biofeedback, self-hypnosis or tai chi) except individuals who have been already on continuous therapies for at least three months Exclusion Criteria: * Diagnosis of a severe or unstable mental illness that precludes safe participation in the study by a healthcare practitioner such as acute psychosis or mania diagnosed by a healthcare practitioner * Current suicidality risk as indicated during the conduct of the Columbia Suicide Severity Rating Scale (C-SSRS) (21) with concurrence after a study physician's evaluation if the response to C-SSRS questions 1 or 2 is "yes"