- Patients fit criteria for chronic pain (CP) if they have had "pain that has lasted longer than three months." As per the International Association for the Study of Pain (IASP) taxonomy of CP syndromes, this includes: "relatively generalized syndromes," "relatively localized syndromes of the head and neck," "spine and radicular pain syndromes," "local syndromes of the upper limbs," and "visceral pain syndromes."