A Dietary Supplement. Each tablet contains 64 mg of Elemental Magnesium. Slow-Mag is the Magnesium supplement that provides: Magnesium chloride for increased absorption versus magnesium oxide; Enteric coating to help prevent stomach upset; 212 mg of Calcium Tablets are the simple, effective way for them to get the magnesium they may need. Slow-Mag is a magnesium chloride supplement with a protective enteric coating and 212 mg of calcium per serving. 128 mg magnesium + 212 mg calcium. Slow-Mag Tablets use magnesium chloride for higher bioavailability. Enteric coating helps prevent stomach upset.