My old lab, Harry was on Cosequin for years for arthritis. I was a bit sceptical at first but it tranformed him and gave him a new lease of life. After a few years it wasn't quite enough and he had to have Metacam too but it kept him going for quite a while. I started off getting it from the vet but there was quite a mark up on the price. In his latter years I bought it from Petmeds onlibne as it was cheaper.
Mambo had that at first when her hips were bad, but it was very expensive. She now has 4wkly catrophen injections and Rimadyl to top up and daily Chrondroitin and Glucosamine, Last check up Vet very pleased and says she should make old bones!! (she is 5yrs old now)