Methodology. The investigators propose to use a randomized, controlled, double blind study design to examine the effect of adding topiramate (TOP) to a best practice treatment for PTSD, PE. Participants will be 120 male and female Veterans from all services with AUD and PTSD. The investigators' primary aims are to determine the relative efficacy of PE+topiramate, as compared to PE+placebo, in reducing problematic drinking, reducing PTSD symptoms, and improving functioning and quality of life among Veterans with comorbid AUD/PTSD at post-treatment and 3- and 6-month post-treatment follow-up. The investigators will explore the extent to which decreases in drinking and PTSD symptoms lead to improvement in functioning.