
Like everything it depends on the dog. I've known a GSD with arthritis in his awful, awful hips start cartrophen at 2yrs old and last a full 6 months pain free from one course to the next with no additional meds - but my lab lasted less than a month.
I'd definitely recommend acupuncture, I have two having it at the moment and it's made a big difference to them and another one who had it last year. Hydrotherapy as well - just the heat from the water can help even before any exercise is done.
I'd also look at natural painkillers, if he can't have the conventional stuff: turmeric or devil's claw would be my first port of call. Turmeric especially is a highly effective natural anti-inflammatory (DC is also but I find turmeric is often better). Also coconut oil can be very effective, it was the one supplement that helped the above lab until I got her on raw meat and rice and she started responding to other things. Again turmeric was good for her, then. Raw feeding can help too by itself - I can't remember the mechanics behind it but it can help directly with arthritis, it certainly does help her.