Pain (PAIN) is an unpleasant response of the organism to damaged tissue or potential damage, a complex physiological and psychological activity, and one of the most common clinical symptoms. It consists of two parts: nociception and pain response. It consists of the pain sensation caused by an injurious stimulus acting on the organism, and the pain response of the organism to the injurious stimulus (somato-motor and/or visceral-vegetative response, often accompanied by strong emotional overtones). Chronic pain is pain that lasts for more than one month (previously three or six months), and has also been compared to an undead cancer. Currently, there are at least 100 million chronic pain patients in China.