Chronic insomnia is a highly prevalent problem that has not been given due attention in clinical practice. Insomnia is a nonspecific condition characteristic of a number of medical and mental disorders. Differences in sociodemographic and clinical correlates between the insomnia symptoms implied the heterogeneous characteristics of insomnia as defined by the current diagnostic criteria. Insomnia may be compounded by the contribution of comorbid medical disorders and medications used to treat these disorders. The high prevalence rates of insomnia in a number of medical and psychiatric conditions suggest a common pathophysiologic causality shared by insomnia subtypes.
　　Insomnia is associated with increased risk of new or recurrent psychiatric disorders, increased daytime sleepiness with consequent cognitive impairment, reduced quality of life and high healthcare-related financial burden. Emerging data suggest that resolution of insomnia may improve psychiatric outcomes, which underscores the importance of vigorous treatment. In spite of this, insomnia remains underrecognized and thus inadequately treated. Lack of treatment may result in serious psychosocial, economic and clinical consequences. However, the need for a safe, well-tolerated hypnotic agent that relieves sleep problems and does not result in adverse next-day effects has not been satisfactorily met by currently available agents.