My 15 year old collie was on Glucosmine, Chondriotin and MSM tablets for arthritis, but we made the decision at the beginning of the year to put her on Metacam. I think that sometimes there comes a point when a stronger medication is needed. I really didn't want to try veterinary medication but she is so much better (she had started getting thickening of joints in the toes, which have now gone down).
Basically, you know your dog better than anyone , so you'll know if more is needed. Charm (my collie) told us that G, C & MSM wasn't enough anymore, and I think she has done really well considering her age (will be 16 in May) .