Chronic or persistent pain is defined as pain that lasts for longer than six months. Chronic pain can stem from cancer, illness, injury, or postsurgical changes. Often, persons with chronic pain suffer from syndromes that cannot be confirmed by laboratory tests. These chronic pain syndromes include central pain syndromes, fibromyalgia, headache, lower back pain, myofascial pain syndrome, neuropathic pain, and phantom limb pain. Frequent locations of chronic pain include the back, head, joints, chest, abdomen, and extremities. Chronic pain is common and its sufferers are more likely to have anxiety or depression, have poor perception of their health, decreases in their quality of life, and experience a disruption of their livelihood than those who are not in pain.

In most cases, there is no cure for the chronic pain so treatment is aimed at pain control and rehabilitation. Unfortunately, chronic pain is often ineffectively treated because...