18-week, crossover, double-blind, randomized, placebo controlled proof-of-concept study to assess the efficacy and safety of SRX246 (160 mg bid) vs placebo in 52 adult veterans and civilians with a primary diagnosis of PTSD. Subjects will be randomly assigned in a double-blind fashion to 2 groups in a crossover design. The first group will receive SRX246 for 8 weeks followed by 8 weeks of placebo, while the second group will receive placebo for 8 weeks followed by 8 weeks of SRX246. Both groups will engage in a 7-day washout period between treatments. Subjects will be assessed at baseline and then every 2 weeks during the trial using the CAPS.