Hetlioz™ (tasimelteon) is used in the treatment of Non-24-Hour-Sleep-Wake Disorder (Non-24). Non-24 is very common in people who are totally blind because light can not reset their body clock. This causes the internal sleep-wake cycle to be out of sync with the 24-hour day-night. Non-24 is a serious, chronic circadian rhythm disorder in the blind that causes nighttime sleep problems and a wide range of daytime difficulties, including an overwhelming urge to nap.