Glucosamine is an amino acid sugar complex composed of a glucose molecule attached to the amino acid, glutamine, with an acetyl group.
Arthritic joints have been subject to cartilage destruction to the point where bone may rub against bone. Joints become inflammed and painful. Glucosamine stops this process and rebuilds the joint. Glucosamine stimulates the production of joint cartilage and provides the raw material to make it. It also provides the cushioning material in the synovial fluid that lubricates the joint.
Many studies have proven the effectiveness of Glucosamine in arthritis. In the 1980's, 9 placebo controlled studies involving 1500 people showed amazingly effective results. 500 mg taken 3 times daily was associated with a large and significant reduction in joint pain, swelling and tenderness. 
Another European study confirmed that cartilage degradation was being reversed with the use of Glucosamine.
Glucosamine works best when combined with MSM.
Chondroitin is known to absorb water into the joints, it is now believed that chondroitin cannot be absorbed into the body intact and whatever benefits that have been observed were due to Glucosamine. Glucosamine and chondroitin also have antiviral activity. 
Glucosamine is nontoxic, even in doses much higher than are used for arthritis.

DOSE: 1 capsule (500mg) 3 times daily.