Many patients ask about the best type of magnesium supplement to take for the prevention of migraines and other symptoms. Research studies have compared magnesium oxide with chelated magnesium and a slow release form of magnesium chloride and showed that all three types are absorbed equally well. I usually recommend starting with 400 mg of magnesium oxide but chelated magnesium is also very inexpensive and either one can be effective. However, if one type of magnesium causes upset stomach or diarrhea, another one should be tried. Chelated magnesium is a form of magnesium which is attached to an amino acid and depending on the amino acid it is called magnesium aspartate, glycinate, gluconate, orotate, malate, and other. Besides chelated and magnesium oxide, magnesium citrate or carbonate can be tried. When these magnesium salts are not tolerated or not absorbed, slow release forms should be considered, although they are much more expensive. There are two slow release forms, Mag Tab SR (containing magnesium lactate) and Slow Mag (magnesium chloride with calcium). Each tablet of these two products contains only a small amount of magnesium and the daily dose is at least 4 tables. Presence of calcium in Slow Mag may impair absorption of magnesium, making Mag Tab SR the preferred product. People who need to take calcium as well as magnesium should be taking these two separately because calcium interferes with the absorption of magnesium. The reason calcium and magnesium are often combined in one pill (Cal-Mag, Slow Mag, and other) is that magnesium helps improve the absorption of calcium, so it would not be too much to take Cal-Mag with one meal and magnesium alone with another. Patients with serious kidney problems should not be taking magnesium or any other supplements without consulting their nephrologist and having regular blood tests.