I learn from many patients with joint problems that the use of “supplements”, a.k.a. unregulated, generally regarded as safe “vitamins” is quite common. These are not inexpensive, and are available to the consumer in pharmacies and discount stores widely; sometimes they are marketed with names that strongly imply the user is doing something really good for his/her joints!.
Sad to say, this is most likely not true. Glucosamine and Chondroitin sulfate are building blocks of cartilage and our bodies must synthesize them to make the proteoglycans that compose the matrix- without the matrix, there is insufficient water and insufficient lubrication in our joints: we lose cartilage, arthritis supervenes. The concept of providing joints with the raw building blocks of cartilage is not necessarily bad…
But say you are building a house. Parts of the house can be pre-fabricated. If the pre-fab parts are not delivered to the building site, they most likely will not do any good.
There is no evidence that orally administered supplements ever get delivered to the building site. Because they are so readily excreted, they are not regulated as a drug, the FDA allows their sale, and direct consumer marketing takes over. Caveat Emptor!