The International Association for the Study of Pain (IASP) defines pain as an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage. Acute pain resolves within the expected period of healing and is self-limited. Chronic pain persists beyond the expected period of healing and is itself a disease state. In general, chronic pain is defined as extending beyond 3–6 months, although definitions vary in terms of the time period from initial onset of nociception. Cancer pain is in its own special category because of the unique ways neoplasia and its therapies (such as surgery, chemotherapy, or radiation therapy) can lead to burdensome pain. Finally, related to cancer pain, there is pain at the end of life, for which measures to alleviate suffering may take priority over promoting restoration of function.
Pain is a worldwide burden; across the globe; one in five adults suffers from pain. In 2010, members from 130 countries signed the Declaration of Montreal stating that access to pain management is a fundamental human right. The first CDC guidelines on opioid prescribing for chronic pain, including chronic noncancer pain, cancer pain, and pain at the end of life, were published in March of 2016, and continue to be updated.