How do painkillers know where you hurt?

Haven't Got Time for the Pain

Pain keeps us out of trouble. When it isn't busy preventing injury, it's lessening it or reminding us to let it heal. But sometimes pain becomes a nuisance, like an alarm bell that keeps clanging away long after the fire dies out.

One way to mute this din is to cut the signal off at the source. That's ibuprofen's party trick: It stops banged-up cells from ginning up or sending out more prostaglandin. Ibuprofen belongs to a whole category of pain medicines called nonsteroidal anti-inflammatory drugs, or NSAIDs. NSAIDs also relieve the swelling and inflammation that can cause pain. NSAIDs include aspirin and naproxen sodium (aka Aleve) [sources: AHFS; McNicol].

Other analgesics ignore the pain signal but muffle the bell. Acetaminophen, aka Tylenol, works in the brain and central nervous system to deaden pain, although researchers do not fully grasp how it works [sources: AHFS; McNicol].

Both NSAIDs and acetaminophen belong to a category called non-opioid analgesics. Most non-opioid analgesics work by inhibiting cyclooxygenase (COX) or COX-2 enzymes, which kick off the process of converting arachidonic fatty acid found in cell walls into the prostaglandins that activate pain nerves. No prostaglandin means no nociceptor activation and therefore no pain [sources: AHFS; McNicol; Ricciotti and FitzGerald].

For more severe short-term pain, as after an operation, or long-term pain, many doctors turn to opioids. Opioid drugs plug into an existing network of receptors located in your brain, spinal cord and body. Under normal conditions, this system works with your body's naturally produced opioids to control all kinds of processes, including pain. Natural opiates, like morphine and codeine, as well as synthetic opioids, mimic the structure of these naturally occurring neurotransmitters and hijack the system. Like spies who knock out the guards and then man the gates, they keep out other signals, including those associated with pain. They also plug into the body's reward system, producing potentially addictive euphoric effects [sources: Encyclopaedia Britannica; Fine and Portenoy; NAABT].

More intense medical procedures, like surgery, involve general, regional or local anesthesia. General anesthesia involves a mixture of drugs that calms patients, keeps them unconscious, lessens or relieves their pain, relaxes their muscles or blocks their memories from forming. Regional anesthesia locks down sensation from a whole section of the body, e.g., from the waist down, while local anesthesia numbs a small portion, like a foot or spot of skin. This might seem highly localized but, again, the painkiller doesn't know where you hurt -- the person applying it does [sources: Encyclopaedia Britannica; Mayo Clinic].

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