Consequences of insomnia and its therapies.

Insomnia has a number of clinically significant associations. In particular, patients with chronic insomnia have higher rates of psychiatric and medical illnesses, and insomnia is an important risk factor in the development of depression. Insomniacs also have higher rates of health care utilization and reduced quality of life. This article reviews important clinical correlates of insomnia and evidence for possible causal relationships between sleep and health.