Methylsulfonylmethane (MSM or dimethylsulfone) is a high boiling organic sulfone. It is primary used industrially as a high boiling organic solvent for carrying out inorganic and organic reactions. More recently MSM is claimed to have helath benefits for a wide range of medical illness. However, it is not marketed as a medical drug for this would require strict medical testing and studies so it has been sold as a dietary supplement, which doesn't require such strict controls!. There is no evidence that MSM is toxic, but suffers from the problem that as a high boiling solvent it is difficult to remove impurities from MSM solutions and coupled with the fact that is rapidily passes through the skin surface, its danger lies in that is can easily take toxic chemicals into the body.

Glucosamine is also sold as an "dietary supplement", it is a synthetic chemical similiar to the chemcials that the body makes to stimulate the growth of cartilage.

The health claims of glucosamine as a result relate to symptoms of arthritis- pain and swelling. The United States Food and Drug Administration has not approved it to treat arthritis. As such, at this time it is sold as a nutritional supplement and therefore does not need evidence of safety and efficacy.

Formal Chemical Name (IUPAC)
methylsulfonylmethane and (2R,4R,6R)-3-amino-6-(hydroxymethyl)-tetrahydro-2H-pyran-2,4,5-triol

References

http://en.wikipedia.org/wiki/Methylsulfonylmethane

http://en.wikipedia.org/wiki/Glucosamine