Chronic pain is classified as pain that lasts longer than three to six months. In medicine, the distinction between acute and chronic pain is sometimes determined by the amount of time since onset. Two commonly used markers are pain that continues at 3 months and 6 months since onset, but some theorists and researchers have placed the transition from acute to chronic pain at 12 months. Others apply the term acute to pain that lasts less than 30 days, chronic to pain of more than six months duration, and subacute to pain that lasts from one to six months. A popular alternative definition of chronic pain, involving no fixed duration, is "pain that extends beyond the expected period of healing".
Chronic pain may originate in the body, or in the brain or spinal cord. It is often difficult to treat. Epidemiological studies have found that 8% - 11.2% of people in various countries have chronic widespread pain. Various non-opioid medicines are initially recommended to treat chronic pain, depending on whether the pain is due to tissue damage or is neuropathic. Psychological treatments including cognitive behavioral therapy and acceptance and commitment therapy may be effective for improving quality of life in those with chronic pain. Some people with chronic pain may benefit from opioid treatment while others can be harmed by it. People with non-cancer pain who have not been helped by non-opoid medicines might be recommended to try opioids if there is no history of substance use disorder and no current mental illness. If the chronic pain is not relieved, opioids should be discontinued.
People with chronic pain tend to have higher rates of depression and although the exact connection between the comorbidities is unclear, a 2017 study on neuroplasticity found that "injury sensory pathways of body pains have been shown to share the same brain regions involved in mood management." Chronic pain can contribute to decreased physical activity due to fear of making the pain worse. Pain intensity, pain control, and resilience to pain can be influenced by different levels and types of social support that a person with chronic pain receives, and are also influenced by the person's socioeconomic status.
One approach to predicting a person's experience of chronic pain is the biopsychosocial model, according to which an individual's experience of chronic pain may be affected by a complex mixture of their biology, psychology, and their social environment.