How do painkillers work?

How do painkillers work?

• I mean, I know that a lot of it might just be psychological, but it can't all be that. It's not like there's stuff inside the drug to numb your nerves, because then all of ...show more

• Answer:

  There are several known ways that pain medications work. Aspirin, ibuprofen, and other so-called non-steroidal antiinflammatory medications work by blocking an enzyme called cyclo-oxygenase (COX) This enzyme makes an intermediate molecule on the way to prostaglandins, which in turn are used to signal pain. Some non-steroidals (e.g., Celebrex, Vioxx) only block one form of COX called COX-2, so they are supposedly better in terms of not causing internal bleeding (prostaglandins are also used to protect the stomach lining and to control blood clotting). Acetaminophen (Tylenol and others) is similar, but it blocks COX-3 which is mostly in the nervous system, so it blocks pain without controlling inflammation or causing bleeding problems. Prostaglandins are made where the pain is occurring and also in the brain to signal pain, so blocking their synthesis works to control pain no matter where it occurs. There are ways to put the COX inhibitors in the place you want them (think Ben Gay and equivalent -- they have an ingredient similar to aspirin which blocks COX where you put it). Opioids (morphine, oxycodone, heroin, codeine, etc.) bind to receptors which are used by internal signal molecules called endorphins. Endorphins are natural pain control signals that your brain can use to say "all right, already, I get it, you hurt". A lot of the placebo effect is controlled by endorphins (probably also much of the pain control from acupuncture), so when you say that pain control is psychological, that's partially true but it's because your brain and nervous system produce endorphins. This pain control is in the central nervous system, so it blocks pain wherever it occurs. Local anesthetics (lidocaine, Novocaine, etc.) block the actual nerves from the place where the pain is. These don't work unless injected or applied to the surface where the pain is, so they "know where the pain is" by where you put them. Another class of medications basically stimulate the pain nerves so much that they stop being able to signal that you hurt. Capsaicin preparations which you put on a sore place basically deplete the pain neurons of a pain signal called 'substance P', which means that you get a few hours' relief every time you put it on. You pay for that relief with intense burning pain for a few minutes. Come to think of it, "Ben Gay" and its competitors probably use this mechanism as well as putting a COX inhibitor on, and that's what the menthol component is for. There are some research pain medications which are not available for use yet, that block other pain pathways. These include specific substance P receptor blockers and maybe ones which prevent the manufacture or release of substance P. I'm not really familiar with all the research on this.