[8] It is also possible to obtain Mg(OH)2 from seawater using electrolysis chambers separated with a cation exchange membrane.

[9] Most Mg(OH)2 that is produced industrially, as well as the small amount that is mined, is converted to fused magnesia (MgO).

As a laxative, magnesium hydroxide is dosed at 5–10 grams (0.18–0.35 oz), and works in a number of ways.

Furthermore, Mg2+ ions cause the release of cholecystokinin (CCK), which results in intraluminal accumulation of water and electrolytes, and increased intestinal motility.

[12] In 1829, Sir James Murray used a "condensed solution of fluid magnesia" preparation of his own design[13] to treat the Lord Lieutenant of Ireland, the Marquess of Anglesey, for stomach pain.

This was so successful (advertised in Australia and approved by the Royal College of Surgeons in 1838)[14] that he was appointed resident physician to Anglesey and two subsequent Lords Lieutenant, and knighted.

[15] The term milk of magnesia was first used by Charles Henry Phillips in 1872 for a suspension of magnesium hydroxide formulated at about 8% w/v.

It is added directly to human food, and is affirmed as generally recognized as safe by the FDA.

Magnesium hydroxide is marketed for medical use as chewable tablets, as capsules, powder, and as liquid suspensions, sometimes flavored.

This property is attributable to the endothermic decomposition it undergoes at 332 °C (630 °F): The heat absorbed by the reaction retards the fire by delaying ignition of the associated substance.

Because brucite is a swelling mineral, it causes a local volumetric expansion responsible for tensile stress in concrete.

The reaction of magnesium carbonate with the free alkali hydroxides present in the cement porewater also leads to the formation of expansive brucite.