Magnesium oxide is barely absorbed at all - as in studies show absorption around 4%. [1] It's mainly used as a laxative. The only reason it's sold in supplement

Magnesium oxide is barely absorbed at all - as in studies show absorption around 4%. [1] It's mainly used as a laxative. The only reason it's sold in supplements as far as I can tell is it's cheap and supplements are roughly speaking entirely unregulated in America. If you actually want to get the magnesium into yourself, you should use a chelated form like citrate, glycinate, taurate or L-threonate. These are in the 70-100% bioavailability range. L-threonate in particular has been shown to readily cross the blood-brain barrier. Not worth wasting your time and money on oxide or even worse somehow, stearate. [1] https://pubmed.ncbi.nlm.nih.gov/11794633/ https://pubmed.ncbi.nlm.nih.gov/11794633/