MSD Manual

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Overview of Pain

By

The Manual's Editorial Staff

Last full review/revision Sep 2019| Content last modified Sep 2019
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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. The pain receptors are on the ends of long nerve fibers. These fibers carry pain signals to your spinal cord. Other nerves in your spinal cord then carry the pain signals to your brain. Only when your brain processes the pain signals do you actually feel pain.

Sometimes your nerves send pain signals even when you haven't been hurt or injured. This can happen when your nerves have been damaged by a disease such as diabetes (called diabetic neuropathy), or when your nerves were crushed or cut by an injury. Pain caused by nerve damage is called neuropathic pain.

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 or jaw, 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 for having a baby) block pain signals in your spinal cord

  • Pain pills and shots (analgesics), such as opioids and NSAIDs and other non-opioid medicines, affect pain signals all over your body

For neuropathic pain, doctors sometimes have you take an antidepressant or antiseizure drug. These drugs affect nerve signals in a way that relieves pain even if you're not depressed or don't have seizures.

What pain treatments don't involve drugs?

Some pain treatments don't involve drugs.

Transcutaneous electrical stimulation (TENS) applies a gentle electrical current to your skin through a small sticky pad. The current tingles but doesn't feel like a shock. It won't eliminate pain, but it can help some people.

Doctors can also apply electrical stimulation to your spinal cord. They implant a small wire electrode around your spinal cord and send signals that interfere with pain signals.

In acupuncture, practitioners place small needles in certain parts of your body and remove them after a few minutes. They may apply a small electrical current to the needle. These needles seem to help relieve pain, although doctors aren't sure why.

Special mind techniques such as biofeedback, relaxation training, breathing techniques, and hypnosis can help you cope with pain.

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. 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?

NSAIDs are non-opioid pain medicines related to aspirin and ibuprofen. They also block inflammation, such as when a joint is inflamed from arthritis. They aren't as strong as opioids, but 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 non-opioid pain medicines?

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

NOTE: This is the Consumer Version. DOCTORS: Click here for the Professional Version
Click here for the Professional Version
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