Project Summary/Abstract Despite the frequent co-occurrence and deleterious consequences associated with comorbid alcohol use disorder (AUD) and post-traumatic stress disorder (PTSD), there is little scientific evidence available to guide the provision of care. The current study directly addresses this critical gap by testing the efficacy of N-acetylcysteine (NAC) as compared to placebo in reducing AUD and PTSD severity. Accumulating preclinical and clinical research provides encouraging support for the therapeutic potential of NAC in the treatment of AUD/PTSD via glutamatergic modulation. Moreover, NAC is an inexpensive, over-the-counter agent with a favorable tolerability profile. The parent grant is an ongoing 12-week, double-blind, randomized controlled trial testing NAC versus placebo on reduction in AUD symptoms (Aim 1) and PTSD severity (Aim 2). Advanced neuroimaging techniques are employed at pre- and post-treatment to investigate the pathophysiology of AUD/PTSD (Aim 3). All participants receive weekly, manualized cognitive-behavioral therapy (CBT) for AUD. The purpose of this Administrative Supplement (PA-18-591) is to retain Dr. Delisa Brown, a senior postdoctoral fellow, on the parent project for an additional six months to support the successful completion of the study aims and preserve the integrity of the parent grant. Dr. Brown serves in two vital and distinct capacities on the project, and her work in these roles has been delayed due to setbacks resulting from the COVID-19 pandemic. (1) Dr. Brown is a highly-trained Study Therapist, providing weekly CBT for AUD via telehealth to participants. She completed a multi-day training on the intervention theory, background, and implementation, and has participated in weekly supervision over the past two years. Dr. Brown is an exceptional clinician, and as an African American clinician she brings highly valued diversity to the project (almost 20% of the sample is African American). Her work in this capacity will help ensure sufficient power necessary to address Aims 1 and 2. (2) Dr. Brown plays a vital role on the neuroimaging component by conducting imagery script development sessions to create personalized, in-scanner alcohol, trauma, and neutral cues. Dr. Brown completed specialized training at Yale University and Massachusetts General Hospital specifically for this purpose. She also assists with the critical task of pre-processing the imaging data to ensure quality control and preparation for analysis. Her work in this capacity is crucial to the successful completion of Aim 3. The requested Administrative Supplement will ensure Dr. Brown's continued work on the parent grant and maintain the integrity of the highly trained team carrying out this important project. The findings from this project have the potential to innovate clinical practice, improve treatment outcomes, and decrease the significant economic burden associated with co-occurring AUD/PTSD.