Pain is a product of the nervous system consisting of a web of nerve cells that extend throughout the body (the peripheral nervous system or PNS) endlessly gathering information and transmitting it to the brain and spinal cord (the central nervous system or CNS). The CNS interprets the information from the nerves and coordinates the body's response. Perception of pain is a multi-step process, originating with the stimulation of specific nerve fibers . The damaged cells then release chemical mediators of pain and inflammation. The pain stimulus is sent through the PNS to the CNS where the pain message is processed at several levels: a quick response to sharp or acute pain, a slower pathway to the brain for perception of duller, more persistent pain, and the alerting of the autonomic nervous system which regulates involuntary processes such as breathing, blood flow, and pulse rate and signals the release of hormones like epinephrine (adrenaline).

Pain is generally divided into two main types. Acute pain tends to be short-lived with a specific cause and purpose, and generally no persistent psychological reactions. Chronic pain is more complex. It has no time limit, often has no apparent cause and serves no apparent biological purpose. Chronic pain can trigger multiple psychological reactions leading to feelings of helplessness and hopelessness. Some of the most common causes of chronic pain include low-back pain, headache, recurrent facial pain, arthritis pain, neuralgias and neuropathies (diabetic and post-herpetic), and pain triggered by damage to the central nervous system (the brain and spinal cord), among others.

Since there may be other scientific evidence that is not reported in the major U.S. biomedical databases, this list of treatments cannot be considered comprehensive.