The term "opioid" refers to natural, semisynthetic, and synthetic medications that relieve pain by binding to opioid receptors in the nervous system. The term opioid includes all agonists and antagonists with morphine-like activity as well as naturally occurring and synthetic opioid peptides (Miaskowski et al., 2005). Opioids are a mainstay for the management of acute and chronic pain. The use of opioids to manage pain also has been examined in patients with cancer for its effectiveness in managing sleep-wake disturbances.

Miaskowski, C., Cleary, J., Burney, R., Coyne, P., Foster, R., Grossman, S., . . . Zahrbock, C. (2005). Guideline for the management of cancer pain in adults and children. APS Clinical Practice Guidelines Series. Glenview, IL: American Pain Society.