MSM is an abbreviation for a naturally occurring compound called methylsulfonylmethane or dimethylsulfone (DMSO2). MSM is a significant source of the element, sulfur, accounting for nearly 34 percent of its entire weight.  MSM appears as a white crystalline powder and despite being relatively high in sulfur, MSM has no odor. The compound DMSO is chemically related with MSM; being synthesized via oxidation.
The exact mechanism of action for MSM is not fully known. However, MSM does exhibit mild anti-inflammatory and antioxidant activities which may account for many of its clinical effects.  MSM is easily absorbed and enters the bloodstream within hours of consumption.  MSM has demonstrated the ability to cross the blood-brain-barrier as evidenced by magnetic resonance spectroscopy (MRS). 
MSM may play a role in cancer prevention. MSM has specific effects on cellular proliferation and appears to function in a manner similar to aspirin. A study showed that MSM, when combined with aspirin, induced differentiation by a COX-independent mechanism.  The authors suggest that a common mechanism for the chemopreventive action might be the activation of gene functions, leading to differentiation and thereby dismantling the cellular capacity for proliferation.
MSM is found in a variety of foods; including fresh fish, meats, fruits, vegetables, whole grains, and dairy products.  The issue with MSM is that it is quite susceptible to degradation through processing techniques like heating and drying. The highest source of MSM is found in cow’s milk. However, coffee, tomatoes, black tea, Swiss chard, beer, and alfalfa also contain significant amounts. The herb Equisetum arvense, or horsetail, is a good source of MSM as well. 
MSM is popularly known for treating painful arthritic joints. However, there is little evidence to support this application. This does not mean it may not be an effective therapy, as many patients can attest to its clinical effects. There are no published double-blind placebo controlled studies on this use as of yet. Generally, clinical studies of this nutrient are lacking across the board. Preliminary studies of other applications suggest MSM may be a very beneficial therapeutic compound.
MSM has demonstrated efficacy in treating seasonal allergic rhinitis. A multi-center open label trial was conducted among 50 subjects afflicted with this condition.  Patients were administered 2600 milligrams of MSM orally for 30 days Each week, clinical respiratory symptoms and energy levels were assessed by a questionnaire. As well, plasma IgE and C-reactive protein were measured at the beginning and end of the study in all subjects; histamine was also measured in a particular subset. The results showed significant improvements in energy level and respiratory symptoms, with no observable changes in plasma levels of measured markers. The authors conclude that MSM was efficacious at this dosage level. Furthermore, there were few reported side effects.
An animal study indicates that MSM could possibly be administered for autoimmune disease. Rats were given MSM at a dose of 6 - 8 grams per kilogram daily in their drinking water, starting at 1-2 months of age.  The particular rats used were bred to develop autoimmune lymphoproliferative disease. Upon later examination, the lymphoid organs were not as enlarged, and the antinuclear antibody levels were significantly lower than the water-only control group. Researchers speculate that MSM could be beneficial in cases of autoimmunity. Theoretically, supplemental MSM appears to be preventative in action, stressing the need for adequate levels of MSM throughout the lives of humans.
Other conditions for which MSM may be beneficial include; snoring, fibromyalgia, repetitive stress injuries, pain, inflammation, allergies, arthritis, parasitic infections, and the maintenance of normal keratin levels in hair, skin and nails. 
The majority of studies implement an oral dose of 1-3 grams daily, taken in divided doses. Higher doses have also been administered under clinical supervision. Co-administration with vitamin C is purported to enhance the therapeutic effect of MSM.  Clinical improvements are often seen within 2 days to 3 weeks.
MSM is consumed in low levels among most Americans because of the inadequacies seen in the standard Western diet. This type of diet is commonly low in fresh vegetables, fruit and fish, with high intakes of fatty and processed foods. As mentioned, MSM is degraded in processed foods. For this reason, the majority of Americans would likely receive benefit from supplementation.
MSM is generally considered a safe therapeutic substance when taken in recommended doses. The majority of studies reveal few adverse effects in patients taking MSM.
A toxicity study in animals was conducted to evaluate the acute and subchronic toxicity of MSM (Horvath). Rats were given the equivalent of 5 - 7 times the maximum dose recommended in humans. A single dose of 2 grams per kilogram produced no toxicity or mortality. Additionally, a dose of 1.5 g/kg of MSM given daily for 90 days also resulted in no adverse effects or mortality. Upon examination, there were no gross pathological lesions or changes in organ weights; renal histology of treated animals was normal.
1. Anonymous. Methylsulfonylmethane. Alt Med Rev 2003;8(4):438-441.
2. Beilke MA et al. Effects of dimethylsulfoxide on the oxidative function of human neutrophils. J Lab Clin Med 1987;110:91-96.
3. Layman DL and Jacob SW. The absorption, metabolism and excretion of dimethylsulfoxide in Rhesus monkeys. Life Sci 1985;37:2431-2437.
4. Lin A et al. Accumulation of methylsulfonylmethane in the human brain: identification by multinuclear magnetic resonance spectroscopy. Toxicol Lett 2001;123(2-3):169-77.
5. Ebisuzaki K. Aspirin and methylsulfonylmethane (MSM): a search for common mechanisms, with implications for cancer prevention. Anticancer Res. 2003;23(1A):453-8.
6. Balch PA. Prescription for Nutritional Healing: The A-Z Guide to Supplements, 2nd Ed. Penguin Putnam, Inc. New York, NY 2002;184-185.
7. Barrager E et al. A multicentered, open-label trial on the safety and efficacy of methylsulfonylmethane in the treatment of seasonal allergic rhinitis. Altern Complement Med. 2002;8(2):167-73. 8. Morton JI and Seigel BV. Effects of oral dimethylsulfoxide and dimethylsulfone on murine autoimmune lymphoproliferative disease. Proc Soc Exp Biol Med 1986;183:227-230.
9. Jacob SW and Appleton J. MSM: The definitive guide. A comprehensive review of the science and therapeutics of methylsulfonylmethane. Freedom Press. Topanga, CA 2003:107-121. Horvath K et al. Toxicity of methylsulfonylmethane in rats. Food Chem Toxicol. 2002;40(10):1459-62.