Why do opiates make you itchy?

I don't know all the technical terms, so bear with me. Pain and itch have been found to come from the same nerve path. When you take an opioid, it binds the nerve receptor, blocking the pain signal, and releasing the opiate into your system. The theory is that the while the receptor blocks the pain, it doesn't block out the itch. The itch passes through the opiate barrier, and something about the opiate causes the itch nerve impulse to intensify. What your left with is the opiate and the itch traveling through the nerves/receptors. So you feel good and itch like hell!

Some of our cells have receptors for substances called "opiates"- these are chemicals that are either derived from or modeled after opium- a natural substance from opium poppies (that's why you can have a positive drug test after eating poppy seeds, btw)- morphine, heroin, demoral, fentanyl, duramorph, stadol, vicodin, codeine- all are opiates (there's lots of others, too). There are actually 2 types of "opioid" receptors (mu and kappa- impress your anesthesiologist with that bit of info) that are of importance here- and they are found in the central nervous system (i.e. your spinal cord and brain). The reason all those different types of opiates have different affects, one from another, is because they each bind to the receptors differently: some bind for a short time, and so don't last as long, others bind longer and last longer. Some are easier to "pop" off and others harder- some bind more to the mu receptor, some only to the kappa receptor, some to both... all of this relates to how "strong" the drug is and what exactly its total effects are (obviously there's a difference between how you feel after getting codeine vs. shooting up heroin).

Here's where I don't remember the specifics, but suffice it to say, the action of the mu and kappa receptors interrupts your brain's interpretation of sensory stimuli (including pain). They also have the effect of depressing your respiratory function and making your cognitive function less than it should be (in other words, you get sleepy, woozy or high). An epidural or spinal is supposed to avoid those problems because the opiate doesn't reach the brain- just the receptors on the spinal cord, interrupting sensory function (making you unable to feel painful stimulus but hopefully not woozy, etc). Now, again, I don't recall the specifics but either it's part of what the mu or kappa receptor does or it鈥檚 another opioid receptor but there is a receptor that in some people causes an itchy sensation when an opiate binds to it. It's pretty common but not universal and varies widely in severity from person to person (I get very mildly itchy but nothing that bothersome. I know women who itch so badly they have to be sedated).

Yes, that can be a side effect. Especially Oxycontin.

Paramedic in SC

The opiates can trigger a histamine reaction, almost like an allergy. A small dose of Benadryl (diphenhydramine) can alleviate this problem.