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Glucosamine and chondroitin are both substances that occur naturally in the human body. Their primary function is to produce and maintain healthy cartilage, the spongy tissue that cushions bones at the joints. Although researchers are still studying exactly how it happens, glucosamine and chondroitin also appear to play roles at the cellular level in fighting inflammation, retaining water, boosting immune response and blocking some tissue-destroying enzymes.

Glucosamine is an amino sugar derived from the synthesis of glutamine (an essential amino acid) and glucose (blood sugar). It is a component in all connective tissue as well as synovial fluid (joint lubricant). Glucosamine also stimulates production of glycosaminoglycans (GAGs), the primary building blocks of cartilage (material that cushions the ends of bones and also exists separately in joints). It helps provide elasticity and flexibility of joints and also has properties that suppress both inflammation and the enzymes that destroy healthy cartilage.

Glucosamine supplements are usually made from the shells of crabs, lobsters and shrimp. They can also be made synthetically. Manufacturers are beginning to look at a fermentation process involving corn as an alternate source for those who may have shellfish allergies. (However, glucosamine is made from the shells, which contain carbohydrates and not the protein that causes allergic reactions. For more information, see the section Conditions of concern.)

Chondroitin helps form one of the elements of cartilage. Chondroitin supplements are usually made from the cartilage of sharks or cattle (cow tracheas), but can also be made synthetically.

As supplements, glucosamine and chondroitin may be sold separately, but are often found in combined products. They are marketed most often as pain relievers for those with various joint disorders such as osteoarthritis (degenerative joint disease), rheumatoid arthritis and other musculoskeletal conditions (e.g., fibromyalgia). Traditional medical treatment typically involves prescribing nonsteroidal anti-inflammatory drugs (NSAIDs). However, some patients who do not respond to traditional treatment may use glucosamine and chondroitin supplements as complementary or alternative medicine (CAM) therapies hoping they may help relieve the pain and help repair damaged cartilage.

The supplements have also been taken for a variety of other conditions (e.g., AIDS, cancer, Crohn’s disease, inflammatory bowel disease, interstitial cystitis, migraines) based on tradition or scientific theory, but have not been thoroughly tested in humans for safety and effectiveness. Although studies have shown the supplements caused no harm, there is little or no independent scientific evidence about how glucosamine and chondroitin act to relieve or treat many of these conditions.

Results of the most comprehensive study conducted to date on the supplements were announced in February 2006. The Glucosamine/Chondroitin Arthritis Intervention Trial (GAIT), funded by the National Institutes of Health (NIH), found the supplements no more effective at relieving mild pain from osteoarthritis of the knee than a placebo (sugar pill). However, researchers found that those patients with moderate to severe knee pain were more likely to experience relief from symptoms when taking a combination of the two supplements.

A smaller European trial found that glucosamine sulfate offered more relief than acetaminophen or placebo.  Researchers noted that larger studies are necessary to validate the results of these trials.

Experts say it is not clear what optimal dosage of the two substances should be taken when the supplements are combined. The NIH study participants took a daily combination of 1,500 mg of glucosamine and 1,200 mg of chondroitin sulfate.

In Europe, glucosamine and chondroitin are prescribed by physicians and have been used since the 1960s. In the United States, glucosamine and chondroitin are widely available in health food and nutrition stores or via the Internet. No prescriptions are necessary since they are considered food products and not medications. Their dosages are not regulated by the U.S. Food and Drug Administration (FDA).