OBJECTIVE: To report a case of nightmares and sleep disorder associated with improper use of carvedilol, an α/β-blocker, and to model the time course of receptor occupancy in this patient. CASE SUMMARY: A 41-year-old man with panic disorder had been treated with alprazolam 1.2 mg/d (3 × daily), carvedilol 10 mg/d (once in the morning), and etizolam 0.5 mg (for anxiety attack). Although the physical and psychological symptoms gradually improved, he reported nightmares and panic attacks. An interview revealed that he had been taking carvedilol 5 mg twice a day after lunch and dinner on his own initiative, in addition to the prescribed dosage. The patient was asked to take carvedilol 10 mg only after breakfast, as had been advised. Consequently, the sleep disorder and nightmares disappeared. METHODS: We calculated the time courses of β2-adrenoceptor binding occupancy in the central nervous system after oral administration of carvedilol with the ordinary and improper regimens by using pharmacokinetic/pharmacodynamic parameters obtained from the literature. RESULTS: Compared with the ordinary dose of carvedilol 10 mg once a day, the improper regimen (10 mg after breakfast followed by 5 mg after lunch and dinner) increases the β2-adrenoceptor binding occupancy at night (2300) to as high as the mean β2-adrenoceptor binding occupancy after an ordinary dose of propranolol. CONCLUSIONS: The sleep disorder and nightmares experienced by this patient had been induced by elevation of central β2-adrenoceptor binding occupancy at night as the result of improper use of carvedilol.