The primary outcome measures for the efficacy portion of this study are 1) the effective reduction in PTSD symptom severity through the total score on the CAPS at the end of treatment between the two study groups and 2) the effective reduction in the proportion of days using and amount of use of alcohol/substances during the final 30 days of treatment as measured by the TLFB verified by urine drug screens (UDS). In addition, secondary endpoints will include CAPS scores at the 3 and 6 month post-intervention follow-up visits, the 7 day point prevalence abstinence rates at each treatment, post treatment and follow up visits. Also, PSS-SR, Obsessive Compulsive Drinking and Substance Use Scale-Revised (OCDS-R), Addiction Severity Index-Lite (ASI-Lite), Difficulties in Emotional Regulation Scale (DERS), Mindfulness Acceptance and Awareness Questionnaire (MAAS), Five Facet Mindfulness Questionnaire (FFQS) and Cognitive and Affective Regulation Scale (CAMS-R). There will also be secondary endpoints and used to gain insight into potential effect modification and mediation. Secondary analysis will also include the proportion of days using alcohol/drugs, craving, psychosocial functioning and emotional regulation. Participants will be assessed weekly throughout the intervention, at the end of the intervention and at 3- and 6- month follow-ups.