Magnesium carbonate is a magnesium salt. When it contacts stomach acid, it produces carbon dioxide, providing relief from heartburn and indigestion. However, its elemental magnesium content is low, about 28%, and the body absorbs it poorly.
Compared to forms like magnesium citrate or glycinate, magnesium carbonate is less efficient at raising magnesium levels. People typically take it as a powder or tablet for quick digestive relief. High doses can cause diarrhea or stomach upset.