Participants in the treatment group will receive Autonomous Eye movement desensitization and reprocessing (A-EMDR) therapy delivered through an app on their device. Participants will be asked to complete 3 sessions per week for 4 consecutive weeks. During the treatment period, participants will also attend clinical sessions which will focus on factors such as the therapeutic alliance, assessing the participant's current state, reviewing recent alcohol and drug use, reviewing PTSD symptoms, providing a brief counseling intervention, enhancing positive expectancies, inspiring hope, and encouraging adherence to the study protocol.

We will monitor changes in PTSD symptoms using the clinician-administered PTSD Scale DSM-5 (CAPS-5)/PTSD checklist for DSM-5 (PCL-5) from baseline to weeks four and eight. We will monitor overall alcohol and drug consumption and cravings using the TLFB and CEQ, respectively, over the eight weeks period. In line with previous studies, we will use the Brief Coping Orientation to Problems Experienced (COPE) and subjective measures of substance use coping questionnaire (i.e., How many times have you used a problematic substance for trauma-related problems in the last week? 1) to evaluate the exact frequency of substance used for coping with trauma-related problems from baseline to weeks four and eight. The change in these outcomes will be compared between the A-EMDR and TAU groups.

We will assess the feasibility and engagement of A-EMDR by evaluating the rate of retention (number of participants enrolled after deemed eligible, number of sessions completed for each participant, number of participants who withdraw and/or lost-to-follow-up after enrollment in the study) in the group over the four-week treatment period. We will assess acceptability using quantitative scales to determine their satisfaction with the treatment at weeks four and eight.