Question of the Week

How do pain medications target pain?

Sun, 6th Mar 2011

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Andrew McCluskey asked:

Dear Naked Scientists,


I was wondering how Pain relief drugs target pain, and why we don't just go numb in random parts of the body? I hope you can help me in this,




Andrew McCluskey


We put this to Tim Warner from Barts and the London School of Medicine and Dentistry...

Tim -   The explanation for this lies in what causes the pain and how we experience it.  If we imagine, for instance, pain coming from something like a damaged tissue - you could think of something like an arthritic knee for instance.  In that knee, there's a local generation of factors that sensitise the local pain nerve endings.  So that local sensitisation depends upon what's happening locally in the knee and then to the nervous pathways, this is then taken as a signal to the brain where we perceive the pain.  And so, that part of our perception depends on what's happening in the central nervous system. 

So we have that as an idea in our heads.  We can think about how the pain-relieving Pills_painkillersdrugs work.  The non-steroidal drugs that we use for muscle, joint aches and pains, and other drugs like ibuprofen, they stop the formation of the sensitising factors  - in this example, the knee, and only the arthritic knee is making the factors.  Itís only there that the ibuprofen-type drugs act, and so, we feel less pain in our inflamed knee.  And at the same time, the other knee doesnít go numb because it isnít making the sensitising factors.  So there's nothing there for ibuprofen to inhibit. 

If you had a more intense pain, say an operation on your knee, so you might use something stronger such as a morphine type drug, and those ones do work within the central nervous system.  So those drugs are going to cut down the signals in the brain, coming from the nerve collections in the knee, and so, they cut down the sensation of pain by a central effect in the brain, and not by acting locally in the knee like ibuprofen.  But because they act centrally, they have a tendency to also generally dampen down pain pathways.  So to some extent, you may have a feeling of numbness somewhere else.


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Pain relief drugs (like aspirin and ibuprofen) don't actually 'target' spots in your body, they simply are dispersed around your whole body and thus the part of your body (brain) that is experiencing pain will be numbed. The drugs are designed not to have adverse effects as they move about your body, but because they are so general and because your body treats them essentially like a foreign substance, your body can become accustomed to processing these chemicals and over time will become quite efficient at moving the substance through the various filters in your body (e.g. liver) and the drugs will essentially become less effective because your body has become more effective at getting rid of them. Tay, Wed, 2nd Mar 2011

come to see.Thanks amanda25, Thu, 17th Mar 2011

There are at least 2 types of pain medications: 1) aspirin, tylenol, etc. which reduce inflammation 2) narcotics opiods which work on pain receptors in the brain. all pain comes from the brain, not the body part that is inflamed or injured. billferguson, Sun, 27th Mar 2011

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