Be Careful! I have read that many glucosamine supplements contain high levels of mercury. That is right. Most of the glucosamine sold on the market is from China where quality control is lax to non existent. We know that glucosamine is from shells of crab, shrimp and lobster (mainly crab). If you think the waters here are polluted just imagine how they are in China where there are almost no laws against pollution. Chances are, that is where your glucosamine comes from and then the manufacturer puts some fancy label on it and you think nothing of it. If you do not believe me check out this website that explains it all In terms of glucosamine products, I would say that Cosamin DS is about the best on the market. It has been studied by the US government and prestigious universities such as Harvard and Stanford. Glucosamine works best within chondroitin which is from cattle tissue. I emailed the maker of Cosamin about where the raw material to make the glucosamine is from but have not heard back as of yet. I do know that they manufacture their product in the US. I believe very soon a lot of people taking Glucosmaine will be found to have high levels of mercury in their body and will be surprised because they do not eat a lot of fish. We know that fish has high levels of mercury and just imagine what Chineese seafood has in it. Be careful and choose only the highest quality glucosamine supplements!