I have the same resisitance, and for a long time I just thought it was me, and then finally an anesthesiologist and a pharmacology professor told me that were a good many people who were naturally resistant to opioids just like there are others who are naturally susceptible and who, as a result, are more susceptible to addiciton to them. Drugs containing opioids or derivatives don't do a thing for me when administered for pain (I wouldn't take them recreationally). Consequently, my favorite pain medicine is ibuprofen.

I believe I read somewhere on here that cannabis is supposed to contribute to making opioid receptors more sensitive, which is why some folks believe it to be a gateway drug to addiction to harder substances like heroin. I don't know if that's true or not, but I do know there are folks who are resistant to opioids because I'm one of them, too.