This medication is a mineral supplement used to prevent and treat low amounts of magnesium in the blood. Some brands are also used to treat symptoms of too much stomach acid such as stomach upset heartburn and acid indigestion. Magnesium Chloride is an over-the-counter medication used to prevent and treat low amounts of magnesium in the blood. Magnesium is essential for the normal functioning of cells muscles bones nerves and the heart. This medication is available as an injectable solution and is not covered by Medicare.