Background/Purpose: A significant increase in the prescribing of nonbenzodiazepine hypnotic agents (z-hypnotics) has been noticed in the past decade. Several safety concerns have emerged after the excessive use of z-hypnotics. This study aims to characterize the z-hypnotics users with a focus on those with overlapping duration of z-hypnotics supply by using Taiwan's National Health Insurance Research Database. Methods: Incident z-hypnotic users who received at least one z-hypnotic prescription from outpatient settings during 2001–2010 were identified and classified into three groups: duplicated users (those who received multiple z-hypnotic prescriptions on the same day), suspected duplicated users (those who received multiple z-hypnotic prescriptions with 7+ days of overlapping supply), and nonduplicated users. We examined the demographic profiles of these z-hypnotic users as well as z-hypnotics prescriptions (duration, daily consumption, and characteristics of providers). Results: We identified 242,412 incident users of z-hypnotics with 2.4 million z-hypnotic prescriptions during the 10-year study. Almost 20% of them were duplicated (n = 29,948) and suspected duplicated users (n = 16,899). Duplicated and suspected duplicated users were more likely to be male and in their old age compared to the nonduplicated users. Approximately half of the suspected duplicated users (51.8%) and nonduplicated users (47.0%) received their z-hypnotic prescriptions from primary care clinics while duplicated users received their z-hypnotic prescriptions from metropolitan hospitals (29.9%) and academic medical center (26.2%). Duplicated z-hypnotic users were more likely to receive more days' supply and higher daily dose of z-hypnotics. Up to 31.0% of duplicated z-hypnotics users received > 1 defined daily dose/day if adding all prescriptions they received within 1 day. Conclusion: Duplicated z-hypnotic users were more likely to receive prescriptions with long duration and high daily dose. Healthcare professionals and policy makers are recommended to put more efforts into dealing with this urgent drug safety issue.