As there are so many joint supplements on the market containing Glucosamine and Chondroitin, I thought the following website might be of interest.

www.icne.co.uk

It appears that some of the products don't contain what is claimed on their label.

Three quoted examples are:
Superdrug Glucosamine & Chondroitin, the product only contained 95% of the claimed Chondroitin and 79% of the Glucosamine.
Nature's Aid High Strength Glucosamine & Chondroitin contained 91% of the claimed Chondroitin and 67% of the Glucosamine.
Vitamins Direct High Stregth Joint Supplement contained 0% of the claimed Chondroitin and 110% of the Glucosamine.

The website is well worth a look and I will be ringing them over the next few days to let them know their link to the tested products isn't working.