Do not get confused between the two. MSM provides organic sulfur and is a nutrient. Sulfa-based drugs, also known as sulfonamides, do not occur naturally and are used as antibiotics. The sulfa molecule is much larger and can cause severe reactions in some individuals. While many people are allergic to sulfa drugs, no similar reactions have ever been reported with MSM. A third sulfur-containing compound, known as sulfites, is a form of preservative that can cause allergic reactions in some individuals. MSM does not contain sulfites, and should not cause a reaction in sulfite-sensitive individuals.