Firstly, take him to the vet for a proper assessment. Make sure he's carrying no extra weight - as that's extra stress for his joints. If he has arthritis that should be treated and managed, and is a whole other story, and might want to include things like hydrotherapy. There is limited evidence base for glucosamine as a supplement but many people (including us) feed it as a supplement - make sure you get the canine formulation, not the human. Synoquin is the brand we get. I'm sure one of the vets on the board can comment on the latest thinking on supplements. Other things you can do include making sure diet includes oily fish, eggs etc. Check his bed - you might want to consider something like an orthopaedic bed. In winter make sure he is nice and warm and out of any draughts.
The answer to the human question is that human supplements are Glucosamine Sulphate whilst dog supplements are Glucosamine Hydrochloride it is to do with different digestive systems being able to absorb the different forms. Glucosamine Hydrochloride is more bioavaliable to the dog than the human form. Macdog I am afraid the supplement you recommended is Glucosamine Sulphate and you need to feed it at roughly 10 times the human dose to have the same amount of Glucosamine avaliable in the body as the dog supplements.
Scuttlebutter/Istillfeelsecenteen - our vet told us that the glaucosamine you can get from the supermarket/pharmacy is just the same as the stuff they'd prescribe (but much much cheaper!) and that we're fine to use it with our old lady. She's been on it a few of years now (she's 15) and it's been helping with no problems.
The ladies who run the hydrotherapy pool our Lab goes to say that the salmon oil is fantastic. We have got some but our girl has been poorly with cancer and her arthritis has taken a back seat so she hasnt had any lately. Definitely worth a try though.
The supplements they have seen clients use that seem to have shown improvement include that salmon oil, glucosamine, chondroitin, green lipped mussel, turmeric, boswellia and a supplement that contains a mix of goodies called Joint Aid. Dont know whether its worth doing any research into some of those?
Our dog didnt respond to glucosamine/chondroitin whatever formulation we tried. For her, hydrotherapy and acupuncture which have both been truly wonderful, combined with non steroidals help to keep her comfy.