Despite the overall improvement in PTSD symptomatology with CPAP therapy, adherence to CPAP is far worse in Veterans with PTSD (41%) compared to the general population with OSA (70%). Among the factors associated with CPAP non-adherence is the coexistence of insomnia. Complex insomnia defined as the coexistence of comorbid insomnia ans OSA is a frequent diagnosis in military personnel with combat exposure. Similar to prior reports of patients with OSA without PTSD, comorbid insomnia can create a barrier to CPAP therapy. Ramelteon (TAK-375), approved by the Food and Drug Administration for the treatment of insomnia with sleep onset abnormalities, is a neurohormone that functions as a melatonin receptor agonist targeting the MT1 and MT2 receptors located in the suprachiasmatic nucleus of the hypothalamus which regulates the circadian rhythm of the 24-hour sleep-wake cycle.The goal is to test the hypothesis that the administration of insomnia therapy-ramelteon- significantly improves treatment outcomes in Veterans with PTSD and complex insomnia compared with placebo.