Good question. The law makes little distinction between drunk driving, impaired driving due to pain meds or using a cell phone (which is proven to be Worse that driving Drunk!)--although I am only aware of the Sandy City restrictions on driving & cell phone use. A person could be pulled over, cited or arrested for doing any of these while driving.
Personally I have a bad back and it has been that way since the early 1980s when I ruptured two discs in my low back at work. I am able to take much larger doses than most people when it comes to pain meds before they really affect me or relieve pain. I also try to use pain meds as little as possible so that a) I don't get addicted and b) so that I become immune to their effects and c) so I don't worsen the condition of my body due to the side effects these drugs do have associated with them.
That said, though I can walk about a 1/4 mile max on most days at any given stretch without having disabilitating spasms and excruciating pain, they happen. Am I taking meds-no, very infrequently. So for me this means that I will carry most of the time and not worry about it. The fact that my disability presents problems associated with pain is no deterrent
to my carrying. I would rather be with my faculties about me than be hopped up on pain meds unless absolutely necessary.
I recently had surgery on both wrists & wasn't able to carry, but I was taking percoset and I erfused to even drive if I was taking them. So perhaps staying in is sometimes the best option. But most of the time I wouldn't sweat it.
I think a lot relies upon ones ability to not only recognize they could be affected with impaired responses, but also the cognizant ability to make good decisions on how, or even when they will carry when using any legal drug. The best thing to do is see how they affect you first and then use that as your measure. If it clouds you or slows you, or makes you tired I would not suggest carrying. But is it helps you to be able to function and doesn't affect judgement or anything else then you should be ok.
This is how I do it.