Analgesics are drugs designed specifically to relieve pain. Opioid (also called narcotic) analgesics work by binding to receptors on cells mainly in the brain, spinal cord and gastrointestinal system. Opioids are often very effective against pain, but they also carry a greater risk of side effects than acetaminophen.

There are several ways to categorize pain. One is to separate it into acute pain and chronic pain. Acute pain typically comes on suddenly and has a limited duration. It's frequently caused by damage to tissue such as bone, muscle, or organs, and the onset is often accompanied by anxiety or emotional distress.
Chronic pain lasts longer than acute pain and is generally somewhat resistant to medical treatment. It's usually associated with a long-term illness, such as osteoarthritis. In some cases, such as with fibromyalgia, it's one of the defining characteristics of the disease. Chronic pain can be the result of damaged tissue, but very often is attributable to nerve damage.
Both acute and chronic pain can be debilitating, and both can affect and be affected by a person's state of mind.

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