Magnesium Chloride Hexahydrate LR AR is an over-the-counter medicine used to prevent and treat magnesium deficiency. Magnesium is required for normal cell, muscle, bone, neuron, and heart function. Magnesium chloride is a magnesium salt that is offered as a supplement. It is quickly absorbed by the digestive tract and is used to assist increase mineral levels in the blood. It is highly effective for everything from painful muscles to skin rejuvenation. Magnesium is a necessary mineral that is involved in over 300 metabolic activities in the body.