Milk of Magnesia Uses

What is Milk of Magnesia?

A suspension of magnesium hydroxide in water is called milk of magnesia.

Magnesium hydroxide is a white substance that does not dissolve well in water. After standing a while the white floating particles settle to the bottom of the jar. Magnesium hydroxide is part of the medicine called milk of magnesia. The name “milk” is used because of the milky appearance.

List of Uses of Milk of Magnesia

Magnesium is an important element that acts as a catalyst in many life processes. In addition to photosynthesis, it is also required for the oxidation in animal cells that produce energy and for the production of healthy red blood cells. Humans cannot live without magnesium which we acquire mainly from various foods.

Milk of magnesia is an alkaline (basic) water suspension and creamy like suspended form of magnesium hydroxide, Mg(OH)2. It is used as an antacid to neutralize excess stomach acid. Magnesium can also be used in the form of Epsom salts as a treatment for rashes and as a laxative. A more important commercial use of Epsom salts is in the tanning of leather as well as in the dyeing of fabrics.

Indications and Clinical Uses

  • Magnesium hydroxide acts to draw water into the small intestine via an osmotic effect. Fluid accumulation produces distension, which promotes bowel evacuation.
  • Magnesium is used for constipation and bowel evacuation prior to certain procedures. It is commonly used to evacuate the bowl prior to surgery or diagnostic procedures. Onset of action is rapid.
  • Magnesium hydroxide also is used as an oral antacid to neutralize stomach acid. In large animals it is used as an antacid and mild cathartic. In cattle approximately 1g/kg as a single dose significantly increases rumen pH and decreases rumen microbial activity.


Magnesium hydroxide has a local effect in the lower GI tract and is absorbed poorly. Approximately 15% to 30% of the magnesium in magnesium hydroxide is absorbed in the small intestine. Onset of action is 30 minutes to 3 hours after administration. Low dose administration produces effects in 6 to 12 hours, whereas high dose administration produces effects in 2 to 6 hours. Excretion occurs in the kidneys and GI tract.


Magnesium hydroxide is a salt. It works in the small and large intestine by attracting and retaining water in the intestinal lumen, thereby increasing pressure within the intestine. The retention of fluid in the intestine results in stimulation of the stretch receptors and an increase in peristalsis which promotes evacuation of the bowel.

Adverse Effects

Adverse effects can occur with large doses. Overactive bowel is the primary adverse effect. Fluid and electrolyte imbalance can occur with large doses given frequently.

Drug Interactions

Magnesium hydroxide may decrease or increase the effects of many drugs. Magnesium salts must be used with caution in patients with renal failure because retention of magnesium could result in magnesium toxicity. Safe use in children younger than 2 years of age has not been established. Large doses in pregnancy may lead to serious fluid and electrolyte imbalance.

Frequently Asked Questions on Milk of Magnesia

Is Milk of Magnesia a good laxative?

Magnesia milk is a well-known and effective laxative for treating constipation in the short term. People do not use magnesia milk for constipation for more than 7 days at a time, or for other digestive issues for 14 days at a time.

How long does it take for milk of magnesia to work?

Magnesia milk usually works the first time you are taking it. Within six hours you should hope to get a bowel movement. It can happen frequently within as little as half an hour. The existence and cause of your constipation will influence the amount of time it takes for the medication to work.

How quickly does milk of magnesia work?

Magnesia milk usually works the first time you are taking it. Within six hours you should predict a bowel movement. This can happen in as little as half an hour, at times. The type and cause of your constipation can have an effect on how long the medication takes to function.

Does milk of magnesia clean out your system?

People use magnesium milk as a laxative to reduce constipation, and to relieve indigestion and heartburn. Magnesium hydroxide acts to ‘flush’ the contents out by extracting water from the tissue around the intestine.

Which is called milk of magnesia?

Magnesia Milk is a brand name for magnesium hydroxide, a drug used in the treatment of constipation. It is a type of laxative, known as an oral osmotic; it works by drawing water from the surrounding body tissues into the colon. Magnesia milk can be used as an antacid, too.

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