I knew the risk when I gave mine previcox but nothing else would work. Without it he struggled to stand up, when he was on Previcox I would walk him for between 1 and 2 hours a day and he could run at full speed (good for an 8 year old mastiff!). It was a choice, a shorter life of decent quality, or a longer one where he struggled to walk and couldn't run. The choice was easy, he loved his walks far too much to be lame!
I would only use them if there's no alternatives though.