The α1-adrenergic antagonist prazosin has showed good effect against posttraumatic stress disorder-related nightmares in several randomized controlled trials. The α1-adrenergic antagonist doxazosin, which has a longer half-live than prazosin, has received far less attention in the treatment of such nightmares. Here, we report a case of a patient suffering from severe nightmares following an erroneous medical administration of adrenaline (causing severe physiological hyper-activation) who was treated with doxazosin. Over a period of 280 days, the patient kept a nightmare diary and took 0, 4, or 8 mg doxazosin. The analyses showed that 8 mg doxazosin (55.2% nightmare-free nights) worked better (odds ratio = 28.2; 95% confidence interval = 3.7-213.9) compared to nights without doxazosin (4.3% nightmare-free nights). Except dizziness, which was not regarded as particularly bothersome by the patient, doxazosin was well tolerated. It is concluded that doxazosin may be indicated as a pharmacological treatment for patients suffering from posttraumatic stress disorder-related nightmares.