Glucosamine has been used recently to treat arthritis. The idea is that since glucosamine makes up a large part of your cartilage, you can restore the natural health of your cartilage, which protects your bones from grinding against each other. But if you knew basic biochemistry and digestion, you'd think twice.
Glucosamine is comprised of two things - a glucose, and an amino acid (hence glucos-amine).
Glucose is everywhere in your blood. It's what your body gets from food to give you energy. There's no shortage of that there, unless you're starving or a diabetic.
Amine is everywhere throughout your entire body. It is what makes up all your amino acids, which entirely comprise your cell proteins. Enzymes, neurotransmitters, receptors, pretty much anything that your cell makes that directly does something is made up of amino acids.
So there's no shortage of glucose, and no shortage of amines. Your body can get these easily through food, and can break them down from larger molecules. In fact, that's the only way your body survives. If your body can't do that well, you're dying.
In addition, when you digest food or drugs, your body is pretty good at breaking down a lot of it into its