Possible side effects of methylsulfonylmethane, or MSM, include fatigue, headaches, difficulty sleeping, increased severity of allergy symptoms, itching, diarrhea, bloating and nausea, according to WebMD. MSM is considered "possibly safe" for most people when taken orally for up to three months. The safety period is less than 20 days when MSM is combined with other ingredients and applied to the skin.
MSM is a chemical that naturally occurs in humans, animals and plants, notes WebMD. It can also be produced in laboratories and is used to treat a large number of medical conditions including joint inflammation, ulcers, osteoporosis, tendinitis, chronic pain, muscle cramps, headaches, wrinkles, loss of hair, allergies, constipation, gum disease, premenstrual syndrome, obesity, poor circulation, high blood pressure, diabetes, HIV and AIDS, high cholesterol and wounds.
Little scientific evidence exists to support the medicinal use of MSM, according to WebMD. MSM contains sulfur, and deficiency of sulfur has not been observed in the medical literature; there is no recommended dietary allowance for MSM or sulfur. Despite published directions for making drops from MSM to control snoring, no evidence exists that MSM affects snoring. Little is known about the effects of MSM while a woman is pregnant or breastfeeding.
MSM may be effective in lessening symptoms of rosacea, stress, hemorrhoids and osteoarthritis. The substance is possibly not effective for enhancing exercise performance and treating circulatory problems and varicose veins. Insufficient evidence exists to rate effectiveness for other conditions, according to WebMD.