When acute pain progresses to chronic, then it is not a symptom of a condition, but is in itself a condition. It lasts longer than the expected course of the disease or injury. Usual period of 3-6 months. In the past the answer to chronic pain was: “everything is in your mind”. A useful definition by Margo McCaffrey is: “pain is what describes the person who experiences it and exists when he says he exists.” The International Union for the Study of Pain says it is “an unpleasant aesthetic and emotional experience, combined with actual or potential tissue damage, or described in terms of such damage”. Pain is transmitted through the body through the nervous system when nerve endings detect damage to a part of the body. Today, pain specialists can understand how pain is created: the way the nervous system, including the spinal cord, interacts with the brain to create the sensation of pain. Knowledge of the neurotransmitter system, the chemical messengers that transmit nerve signals, has paved the way for important new methods of treating pain. In recent years, scientists have learned how to manage these chemical messengers to change the way they interact with brain signals.