Do not buy them from the Vet!
They will charge you $30+ for a bottle of 10-15 pills, the same thing you buy for yourself for a fraction of the cost.
Our Vet told us to go to Wallmart and buy Glucosamine Chondroitin for "people" in the 500 pill bottle for just a couple bucks. We give one a day to our Border Collie.
Also, do not waste your money on all those jerky treats that claim to have Glucosimine in them. They won't do a thing to help.