Methylsulfonylmethane does not have any known heart side effects as of June 2015, according to WebMD. Some people experience diarrhea, nausea, fatigue, bloating and headache when using MSM. Other side effects include itching, insomnia and increased allergy symptoms.
Taking MSM as a supplement orally for up to 90 days, or combining it with ingredients such as tea tree oil, hyaluronic acid and silymarin to use on the skin for up to 20 days, is typically safe, notes WebMD. Doctors do not know whether it is safe for pregnant or breast-feeding women to use MSM. People use MSM, a chemical that naturally occurs in animals, plants and humans, to relieve a variety of conditions, including rosacea, osteoarthritis, hemorrhoids and exercise-related stress.