Published scientific studies have shown MSM to be safe for human and animal use, for both oral and topical applications. There are no known significant adverse effects or drug interactions. One 100 person study, had 50 subjects taking MSM at 6 grams per day for six months resulted in no adverse effects. Side effects of oral use are infrequent and mild and include mild GI upset and slight insomnia (if taken before sleep).

In 2008 Bergstrom Nutrition®, a U.S. manufacturer of MSM, submitted a notification to the FDA claiming Generally Recognized As Safe (GRAS) status. GRAS is an American Food and Drug Administration (FDA) designation that a chemical or substance added to food is considered safe by experts, and so is exempted from the usual Federal Food, Drug, and Cosmetic Act (FFDCA) food additive tolerance requirements. The FDA responded with a letter of non-objection, functionally designating OptiMSM®, the branded and distilled form of MSM, manufactured by Bergstrom Nutrition, as GRAS. The designation allows the addition of OptiMSM to meal supplement and meal replacement foods, fruit smoothie-type drinks, fruit-flavored thirst quencher type beverages, and food bars such as granola bars and energy-type bars.