Pain relief you can buy at a pharmacy?

Hi, I'm a UK nurse, soon to be moving to the US and I have a question about what we call here "over the counter" meds. My question is.....do most of the pain-relieving tablets bought at the drug store/pharmacy all have the same properties? I've heard of Tylenol, Advil, and a few others, but just wondering, are some more effective than others? And are there any which a nurse should avoid taking whilst working, say if you just have a headache? It's just that I've read quite a few posts about nurses getting into trouble at work because they've taken pain meds.