There are a number of glucosamine products used to treat humans with arthritis. Some brands, such as Synflex are used by both humans and dogs. If you can find a glucosamine product that’s marketed to humans, and it contains the same ingredients as the glucosamine product you are considering for your dog, there’s no harm in buying it. But be aware that there may not be any clinical studies available indicating that the product can be successfully used to treat dog arthritis.