Treatment of chronic pain by long-acting opioids and the effects on sleep.

Chronic pain affects a substantial part of the population, and conveys a huge economic cost to society. Owing to its prevalence and adverse impact, it is of particular interest to clinicians, patients, and the pharmaceutical industry. Conversely, the effects of pain on sleep, sleep on pain, and opioid analgesics on sleep represent a large gap in our understanding, even though pain and sleep are closely linked, inter-related conditions. Chronic pain is often treated by opioid analgesics, which are often thought to promote restful sleep. Indeed it may be assumed that by relieving pain, sleep quality will improve concomitantly. In fact, the reality is much more complicated. The effects of opioids vary according to their formulation and duration of action, and have diverse effects on sleep processes. Despite the prevalence of this problem, there is a surprising paucity of data on the effects of opioids on sleep. This review attempts to summarize the links between pain and sleep, and to look at the studies with opioid analgesics, particularly those with extended-release formulations, that have investigated the effects of opioid analgesics on sleep.