Possible side effects that may occur when taking magnesium supplements include difficulty breathing, flushing, dizziness or fainting, according to Mayo Clinic. Some people may experience muscle paralysis after taking magnesium supplements. When magnesium is injected into a muscle, the injection site may become painful or irritated.
Some side effects may subside after the body becomes used to the magnesium supplements, notes Mayo Clinic. A physician may be able to recommend ways to alleviate unpleasant side effects. It is possible to overdose on magnesium supplements, although it is rare if the kidney is functioning properly. Signs of an overdose include severe drowsiness, a slowed heartbeat and difficulty breathing. Other signs of an overdose include double or blurred vision, a change in urinary habits, fainting and dizziness. Some people may go into a coma after overdosing on magnesium supplements.
People with heart disease or kidney problems should speak to a health care provider before taking magnesium supplements, as they may cause additional health problems, states Mayo Clinic. Some people may be allergic to magnesium supplements, so it is important to inform a doctor about any allergies before taking them. Pregnant or nursing women should consult a physician before taking magnesium supplements. Magnesium supplements may interact with some medicines, so a doctor or pharmacist should be made aware of any other medications or supplements being taken.