Magnesium oxide

Overview

Inorganic magnesium salt. Notoriously cheap, but has a miserable 4% oral bioavailability. Mostly stays in the gut where it acts as a potent osmotic laxative.

Clinical Focus

Do not use Magnesium Oxide to replenish low blood magnesium levels. It does not absorb. Use Magnesium Aspartate or Citrate instead.

Bottom Line

Magnesium oxide is a common oral magnesium supplement and osmotic laxative, but has the poorest oral bioavailability of all magnesium salts and frequently causes diarrhoea.

Brand Names

Various OTC

Oral Routes

Tablets.

Prescribing & PBS

Over The Counter (OTC).

Primary

Historically used for magnesium deficiency.

Clinical Place

Largely obsolete for electrolyte replacement. Only useful if you want to cause diarrhea.