The control of sleep and wakefulness is a complex process involving the coordinated activity of numerous neuronal circuits within small group of hypothalamic neurons that synthesize and release orexins (also known as hypocretins). Orexin receptor antagonists (ORA) differ from benzodiazepines and non benzodiazepines in that they have no effect on GABA and, instead of promoting sleep, these drugs inactivate wakefulness. This results in improved sleep induction and maintenance parameters without producing impairments in cognitive function and other adverse effects permitting daily use on a long–term basis with no risk of rebound insomnia or physical dependence