Pain

Pain is a symptom of being hurt or sick. It is a bad sensation that is physical and emotional.
Most pain starts when part of the body is hurt. Nerves in that part send messages through senses to the brain. Those messages tell the brain that the body is being damaged. Pain is not just the message the nerve sends to the brain. It is the bad emotion felt because of that damage.
The message that the nerve sends to the brain is called nociception. What is experienced because of the nociception is pain.
Kinds of pain
Pain can be acute or chronic. Acute means it only happens a short time. Chronic means the pain lasts a long time.
Pain can be from different types of injury:
Cutaneous pain is from damage to the skin. This is the pain a person feels when their wrist is cut with a knife.
Visceral pain is from damage to the organs inside the body - like the stomach, kidney, and heart. This is the pain a person feels when they have an ulcer.
Somatic pain is from muscles, bones, and joints. This is the pain a person feels when they sprain (twist) a joint like the ankle.
Pain can also happen when there is no underlying injury or cause. Pain can happen just because the nerves do not work right. This is called neuropathic pain.
Treatments for pain
For most pain, the best treatment is to stop the damage that makes the pain. If the ankle is sprained, doctors tell the person not to walk on it. They tell them to put ice on it. This helps the injury stop. For an ulcer in the stomach, doctors stop the acid made in the stomach. This helps the ulcer to heal.
But many kinds of pain also need medicines to feel better. There are many different kinds of medicines for pain:
NSAIDs (acronym for non-steroidal anti-inflammatory drug). These medicines decrease the inflammation where the person is hurt. They also work in the brain to decrease pain. Examples are aspirin, ibuprofen, and naproxen. These medicines can make someone sleepy but they are not addictive. They can cause problems with kidneys and with peptic ulcers.
Opioids are narcotic pain relievers. They do not have the kidney and stomach problems that NSAIDs have. But they can make someone very sleepy and have other potential side effects, such as lack of coordination, inability to concentrate, blurred vision, and weight gain. They can be addictive.
Acetaminophen (e.g. Tylenol) is not a narcotic or an NSAID. So it is much safer than either one, but can cause liver damage.
Anti-seizure medicines (also called antiepileptics or anti-convulsants) - many of these medicines work for chronic neuropathic pain. Other pain medicines may not work at all for those kinds of pain. Examples are carbamazepine and gabapentin.
Anti-depression medicines can also help chronic pain, even if it is not neuropathic pain. This is partly because of an affect on pain itself. But it also helps, because living in chronic pain can cause depression.
There are doctors who specialize in pain management. These are usually anesthesiologists but may also have any one of a number of underlying areas of specialization, such as neurology, physiatry, or internal medicine.
Chronic pain
A new genetic method of treating chronic pain is in the research stage. The idea is to inactivate (turn off) gene HCN2, which plays a key role in chronic pain. Experiments on mice suggest this will work.