People who suffer with anxiety can often have sleep problems as well and the prevalence of insomnia in people with generalized anxiety disorder has been estimated at 43.6%. People who have insomnia are also likely to suffer from anxiety and one study estimated that 32.5% of people with insomnia also suffered from anxiety. Despite this there has been little attempt to investigate the effectiveness of using insomnia drugs alongside ones for anxiety. Researchers in the U.S. studied 383 people with insomnia and anxiety in 41 centres across the U.S. Half were given the anti-anxiety drug escitalopram and a placebo and half were given escitalopram and the insomnia drug zolpidem. Those participants who took zolpidem slept longer and were less drowsy in the day than those taking the placebo but no less anxious. The trial was financed by a drugs company but - according to the journal in which it was published - "the authors of [the] article were fully responsible for the content and editorial decisions and received no financial support."
Fava, Maurizio ... [et al] - Zolpidem extended-release improves sleep and next-day symptoms in comorbid insomnia and generalized anxiety disorder Journal of Clinical Psychopharmacology June 2009, 29(3), 222-230