I'll just throw my 2c in here:
Note: Although I am NOT an expert or a licensed medical doctor, I started my education planning to be a pediatric cardiologist before switching career paths. I also spent nearly 6 years working in the pre-hospital care (paramedic) profession and did several emergency room rotations and advanced training in several other disciplines. As such I studied a great deal about anatomy, physiology, pharmacology, etc., to prepare for those careers. Although I left the medical profession nearly 20 years ago, I still consider myself quite well-informed on this subject.
Based on all my reading and everything I've personally seen, I'm certain that acetaminophen (sold under the brand name Tylenol, as well as other brands and generics) can absolutely harm kidney function, both in short-term overdose situations, and in long-term high-dosage use.
I saw numerous instances of teens OD'ing on acetaminophen, which if absorbed into the bloodstream is considerably more dangerous than narcotic OD's. Many people only crying out for help, never intending to actually commit suicide, have passed away due to kidney failure from something almost everyone has in their bathroom.
Almost all independent research shows long-term use at maximum dosage of acetaminophen can impair kidney function. (Although the same can be said of most NSAID's, I think more research has been done on acetaminophen due to it's popularity.)
It's even worse for people who already have impaired renal function. Unfortunately, most people don't know if they have impaired renal function. (Just like a huge percentage of diabetics are undiagnosed.)
For me, I take acetaminophen at a maximum dose if I have a reason too, but usually no more than 2 dosages in a day, and never for more than 2 days consecutively. It's a rare month I ever take it, though - but if I do, I find adding caffeine with the dosage improves the response to the medication (YMMV). I've never understood why, but for me the combination of acetaminophen and caffeine is much more powerful in relieving pain than acetaminophen alone. I believe Excedrin is still sold in this formulation.
When my spinal condition is really ugly and I need something for pain, I take opioid analgesics. (I already take a daily prescription NSAID for my osteoarthritis, I don't need more NSAIDs in my system.) And yes, I know opioids are habit-forming... I take maybe two dosages a MONTH because of this. I stick with the Vicodin and/or Tramadol that I'm prescribed, refusing to go the route of Oxycodone or something similar. I'd rather be in pain than in a fog.
