Similar to other magnesium oxide products, the MgO-400 from 21st Century is primarily useful for its laxative properties due to the low absorption rate of magnesium oxide. For individuals aiming to address magnesium deficiency for goals like energy, stress, or muscle function, this product is generally not recommended as the body will struggle to absorb a significant amount. The addition of calcium carbonate means it's positioned as a bone health supplement, but both forms are less than ideal for optimal absorption. While affordable, consumers should be aware of its limited systemic efficacy.