How do painkillers work? By reducing the chemical responsible for pain, by reducing the amount of the chemical responsible for pain in the brain, or by blocking the pain signals to the brain.
Painkillers are called analgesics, which comes from the Greek word analgesia, meaning “without pain”. It was first used in reference to painkillers in 1848. There are three main types of painkillers currently used. There are non-steroidal anti-inflammatory drugs, acetaminophen, and opioids. Let’s look at them in turn, but first, what exactly causes pain?
There are three main types of pain: nociceptive pain, neuropathic pain, and functional pain. Nociceptive pain is caused by damage to body tissue. We have sensory receptors in our bodies called nociceptors that connect to nerves. When the nociceptors are triggered, they send a signal to the brain, which is a pain signal. These nociceptors can be triggered by a significant temperature change, such as a burn, or by a mechanical injury, such as a strain, or chemically, which happens when we have an inflammatory response. If the pain is felt in the skin, it is called superficial somatic pain, if it is felt in the ligaments, tendons, bones, or muscles, it is called deep somatic pain, and if it is felt in the organs, it is called visceral pain. Neuropathic pain happens when there is damage to the nerves. If you have a herniated spine, one of the discs in your spine might be pressing on a nerve, which creates pain that can run the length of that nerve. That is why you can feel back pain in your leg. Then there is functional pain, which is pain that disrupts the function of the body and doesn’t have an obvious cause. Pain is usually a signal to us that something is wrong in the body that needs to be fixed, but with functional pain that cause is often unclear.
Non-steroidal anti-inflammatory drugs (NSAIDs) work by blocking the production of a fatty hormone called prostaglandins. When you have a tissue injury, a cut for example, the body’s first reaction is to summon platelets to make the blood clot, sealing off the wound, and then to make fluid leak into surrounding tissue to make the area swell so that nothing can enter the body through the wound while it is being fixed. Prostaglandins have many jobs, but one of them is to make the tissue swell. When there is tissue damage, an enzyme called cyclo-oxygenase (COX 2) is produced, which is necessary to synthesize prostaglandins. Out of the several different types, prostaglandin E2 can trigger the nociceptors, causing the pain response. NSAIDs block the enzyme COX 2, which in turn blocks the prostaglandin. This reduces the inflammation and reduces the pain. These painkillers do have side effects because there are a lot of good and necessary prostaglandins in the body as well. A big problem is in the stomach and the intestines where prostaglandins stimulate the mucus that protects the stomach lining from its own acid. Without this mucus there can be bleeding or even ulcers.
Acetaminophen is more commonly known as paracetamol or Tylenol, and it is the second type of painkiller. It is unusual in the fact that nobody seems to know exactly how it works. The predominant theory is that it works to block the COX enzyme, but probably in the brain and spinal cord. It blocks the production of prostaglandins, but in a different place. Because of this these painkillers don’t reduce inflammation and there are very few side-effects because they work in specific places.
Opioids are the strongest type of pain relief available, but they have several side-effects, and they can lead to addiction. They work by binding to opioid receptors in the nerves. These receptors are right where the synapse sends a pain signal to the next part of the nervous system. When the opioid has bound to the receptors, the signal can’t get passed and the pain signal does not reach the brain.
Different painkillers are used for different types of pain and sometimes they are mixed together to get the best of both worlds. Each type of drug takes a different amount of time to start working and some of them last longer than others. Obviously, for the sake of safety, the painkillers you can buy over the counter are not as strong as the ones you get with a prescription from your doctor. And this is what I learned today.
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Sources
https://mychyp.org/post/What-are-Functional-Pain-Disorders
https://www.healthline.com/health/pain#causes
https://www.beaumont.org/services/pain-management-services/nociceptive-pain
https://www.physio-pedia.com/Nociception
https://www.msdmanuals.com/home/brain-spinal-cord-and-nerve-disorders/pain/overview-of-pain
https://www.etymonline.com/word/analgesic
https://www.medicalnewstoday.com/articles/prostaglandins#function
https://en.wikipedia.org/wiki/Prostaglandin_E2
https://journals.physiology.org/doi/full/10.1152/physrev.00004.2008
https://www.vinmec.com/eng/article/how-do-pain-relievers-work-en
https://www.medicalnewstoday.com/articles/how-does-pain-medicine-work#opioids