Chronic pain is pain that persists beyond the expected time of healing. The time course for the development of chronic pain is variable, and arbitrary time classifications (e.g., longer than 6 months) will often be inaccurate. The ongoing pain itself has now become a significant disease process, not just a symptom of a disease process. The transition to chronic pain is marked by changes in both physiological and psychological responses. Instead of trying to escape the painful situation, the patient is now trying to adapt to ongoing pain.

The neuroendocrine stress response is typically exhausted in chronic pain states, and catecholamine induced changes are now absent. Vegetative responses predominate, including sleep disorders, irritability, depression, and decreased motor activity. Patients often appear subdued, sleepy or sad in appearance.

Psychological factors are important in chronic pain. Withdrawal and depression are common, causing severe strain on social and family support systems. Narcotic tolerance is frequent, further complicating the treatment of this patient group.

While chronic pain can be somatic or visceral, it is very often neuropathic in nature. Nervous system tissue has been damaged, and abnormally maintains the sensation of pain without any external stimulus. Neuropathic pain is usually associated with some form of sensory deficit, and is described as typically raw or burning in nature.

Unlike acute pain, narcotics alone are usually ineffective in relieving chronic pain. Treatment of chronic pain states involves the use of antidepressants, anticonvulsants, and/or corticosteroids. Additionally, diagnostic and therapeutic nerve blocks can be helpful.