Methylsulfonylmethane, more commonly called MSM, is a compound that occurs in some plants. It also appears in trace amounts in many of the foods we consume, and though MSM supplements are marketed as "dietary additional," medically, they haven't been proven to be effective.
MSM nutritional supplements are marketed as sources of sulfur. This marketing goes against the fact that protein is a source of sulfur and that, in general, people are not lacking for sulfur. Thus the effectiveness of MSM supplements is questioned. Only a few studies have been done, so while MSM is sold as a health supplement, some dispute its actual helpful effects. Part of this is because the actual effects of MSM aren't really understood. Some research shows it may have anti-inflammatory effects. MSM may also help remove toxins in the body by bonding with them and helping them move more quickly through the urinary tract.
Another clinical test points to using MSM supplements to help with osteoarthritis and other joint issues. Again, though, there have only been pilot studies done in this area. Other illnesses and diseases that appear to benefit from MSM supplements are hay fever, interstitial cystitis and, most surprisingly, snoring.
With such possible benefits, however, generally come side effects, but in the published research done with MSM supplements, no serious side effects appeared. There is currently no data on MSM's long-term effect, however, so it's unknown if using MSM for a long period of time will have any side effects or cause any other issues. So far, unlike other sulfa-based drugs, MSM has been shown to be completely safe.
If you do find that your body is low in sulfur (which can happen depending on your diet), you'll find that your body takes longer to heal and may, in fact, produce damaged cells that cause their own illnesses. Your hair and nails may become brittle, and you may feel more pain from actions than you previously did since sulfur helps us handle our sensitivity to pain. If you suffer from any of these symptoms, you may want to take MSM supplements. Always consult your doctor, however, before starting on a new dietary supplement.