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Overview of Pain


The Manual's Editorial Staff

Reviewed/Revised Jun 2023
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Pain is an unpleasant feeling that tells your body you might be injured.

What causes pain?

Injuries, such as cuts, burns, fractures, sprains, and bruises, activate pain receptors around the injury.

  • Pain receptors are on the ends of long nerve fibers

  • Fibers carry pain signals to your spinal cord

  • Other nerves in your spinal cord then carry the pain signals to your brain

  • You feel pain only when your brain processes the pain signals

Referred pain is when pain from one part of your body is felt in a different part. For example, pain from a heart attack is usually felt in your chest, because that's where your heart is. But sometimes a heart attack causes pain in your neck, jaw, or left arm because pain signals from those areas travel along nerves that are near the nerves from your heart.

Anxiety, depression, or sleep problems can make pain more unpleasant than it would normally be.

How do doctors treat pain?

Doctors first treat the problem that's causing your pain. For instance, if you have a broken bone, they'll set it and put on a cast.

They also may give you medicine to stop the pain. Different types of medicine work on different parts of the pain pathway:

  • Numbing (anesthetic) creams and gels go on your skin to block pain receptors

  • Numbing shots in your skin or along major nerves block pain signals in those nerves

  • Numbing shots around your spinal cord (such as an epidural Pain relief for having a baby) block pain signals in your spinal cord

  • Pain medicines taken by mouth or as a shot (analgesics) affect pain signals all over your body

What pain treatments don't involve medicines?

Some pain treatments don't involve medicines.

What are opioids?

Opioids are the strongest pain medicines. They’re called opioids because they first came from the opium poppy. Some opioids still come from plants, but many are made in a lab. There are many different opioids, including morphine, oxycodone, fentanyl, and codeine.

Opioids are good for relieving really bad pain, such as from a burn, broken bone, or cancer. But opioids can have serious side effects so doctors try not to use them for less severe problems.

What are the side effects of opioids?

Opioids make you sleepy and relaxed. If you take too much you may:

  • Become very confused

  • Pass out

  • Stop breathing and die

Many people die each year from accidental opioid overdose.

Other common side effects of opioids include:

  • Nausea (wanting to throw up)

  • Constipation (can't poop)

  • Itching

Will I get addicted to opioids?

Opioids make you feel good. Once you start taking an opioid, it can be very hard to stop. That can lead to a substance use disorder Substance Use Disorders The use of some substances (like certain drugs) causes feelings of pleasure. The pleasure makes you want to keep using the substance. The substances can be legal drugs such as alcohol and tobacco... read more . One reason it's hard to stop is that you get drug withdrawal symptoms.

Opioid withdrawal can develop even if you take opioids for less than a week. Withdrawal is worse the longer you take the drugs. Symptoms of opioid withdrawal include:

  • Feeling anxious and jittery

  • Runny nose and watery eyes

  • Yawning and sweating

  • Stomach cramps, nausea, and vomiting

Fortunately, opioid withdrawal won't kill you.

To minimize your chance of developing addiction, doctors:

  • Use opioids only for pain that can't be controlled with other treatments

  • Prescribe opioids for as short a time as possible

What are NSAIDs (nonsteroidal anti-inflammatory drugs)?

NSAIDs are pain medicines such as aspirin and ibuprofen. They are not opioids. They relieve pain and block inflammation, such as in joints inflamed from arthritis. Although they aren't as strong as opioids, they're very effective.

What are the side effects of NSAIDs?

Unlike opioids, NSAIDs don't make you sleepy or stop breathing. However, NSAIDs can:

  • Irritate your stomach and cause pain

  • Increase risk of bleeding, such as from your stomach or in your brain

  • Cause fluid retention and kidney problems

  • Some NSAIDs increase risk of heart attack and stroke

What are other pain medicines?

Acetaminophen (Tylenol) is a very common pain medicine. It's not an opioid and is about as effective as NSAIDs, but doesn't irritate your stomach or increase risk of bleeding. However, too much acetaminophen can damage your liver.

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