How hard are painkillers on liver and kidneys?

I have been taking darvocet 100n for over 2 years for a chronic condition. But what i am worried about, I didn't want to take anything stronger ( most docs don't want to give anything anyways) , so now I have to take 2 or 2.5 pills to get any relieve, which I know is way to much. But when you are hurting , you don't care. What are the first signs that i am hurting my kidneys or liver? Latest bloodwork didn't show anything ...please help.