Denes Greenleaf, they are homeopathic and you can start with a higher dose (3 twice a day) then gradually reduce as they start to work.
Also recommend the Bioflow collar, although the only drawback (if you can call it that) is you don't notice the dogs going downhill so much, until the day they go off their legs.
You can get them off ebay cheaper, as the agents are supposed to sell them at a set price, but as said above, make sure they are genuine Bioflow. Try not to give Metacam long term as it messes up their insides.