Written Exposure Therapy (WET) plus Treatment As Usual (TAU). WET is a 5 session, evidence-based trauma-focused written narrative exposure treatment. At each session, patients are instructed to write about the same trauma event and therapists provide feedback about adherence and offer suggestions. The first session includes psychoeducation about PTSD and a treatment rationale prior to general trauma narrative writing instructions, and specific instructions for completing the first writing session, before completing the first writing (30 minutes) session. Participants are instructed to write about the same trauma event at each following session, with an emphasis on delving into their deepest emotions and thoughts, in as much detail as possible, about the event. All writing sessions begin with specific instructions from the therapist followed by 30 minutes of writing by the participant.

Treatment As Usual (TAU) augmented by a neutral topic writing condition. The neutral topic writing condition involves writing about an assigned topic during each of the five writing sessions. As opposed to writing about trauma, the specific focus of this condition is on writing for 30 minutes about topics related to their life without writing about emotions or opinions. Rather, they are asked to write about specific objects or events in detail, as accurately as possible, and with as much description as possible. All writing sessions begin with specific instructions from the therapist followed by 30 minutes of writing by the participant.

Written Exposure Therapy is a 5 session treatment in which individuals write about their trauma event in a specified manner.

PTSD Checklist for DSM-5 (PCL-5) will be used to collect information on PTSD symptoms. The PCL-5 for DSM-5 is a 20-item self-report measure, selected for its dimensional sensitivity, with higher scores reflecting greater PTSD severity. Scoring is based on how much the patient has been bothered by the symptoms on a scale from "0 = not at all" to "4 = extremely." PCL scores will be collected based upon symptoms experienced in the past month at Baseline as well as each Post-Baseline Follow-up (8-weeks and 12-weeks), while the weekly PCL-5 will be administered at each of the five writing sessions and post-treatment (after 5 writing sessions) assessment. PCL-5 total symptom severity scores range from 0 to 80 with higher scores indicating greater PTSD severity.

PTSD Checklist for DSM-5 (PCL-5) will be used to collect information on PTSD symptoms. The PCL-5 for DSM-5 is a 20-item self-report measure, selected for its dimensional sensitivity, with higher scores reflecting greater PTSD severity. Scoring is based on how much the patient has been bothered by the symptoms on a scale from "0 = not at all" to "4 = extremely." PCL scores will be collected based upon symptoms experienced in the past month at Baseline as well as each Post-Baseline Follow-up (8-weeks and 12-weeks), while the weekly PCL-5 will be administered at each of the five writing sessions and post-treatment (after 5 writing sessions) assessment. PCL-5 total symptom severity scores range from 0 to 80 with higher scores indicating greater PTSD severity.

Timeline Follow-Back (TLFB) will be provided at baseline, and at post-treatment (after 5 writing sessions), 8-week, and 12-week post-baseline follow-up. Calendar-based interviews using the Timeline Follow-Back (TLFB) method will document the frequency of drug and alcohol use for the 3 months prior to baseline assessment, and during the writing sessions (taken at post-treatment follow-up), 8-week, and 12-week post-baseline follow-up. Following baseline, the TLFB will capture days since last assessment (e.g., days between baseline and post-treatment, post-treatment, and 8-weeks, and 8- to 12-week follow-up). Higher numbers of days of use will equal higher substance use.