Magnesium oxide as a laxative

Written by diane evans
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Magnesium oxide as a laxative
Magnesium oxide acts both as an antacid and a laxative, relieving heartburn, acid indigestion and constipation. (medicine image by Pali A from

Magnesium oxide is commonly used as an antacid or a laxative. It is absorbed slowly in the human body, producing a bowel movement with possibly some diarrhoea as a minor side effect. Its chemical formula is MgO, meaning the molecule contains one atom of magnesium and one oxygen atom.


Magnesium oxide is a white, colourless powder that will not dissolve in water. This compound is an effective antacid that will relieve an upset stomach caused by excess hydrochloric acid. Magnesium oxide, which is available without a prescription, comes in the form of tablets or capsules to be taken orally. If you are using it as a laxative, don’t take this medication for longer than one week unless your physician gives you another recommendation. Do not take a dose in the evening or on an empty stomach, but do take it with a full glass of cold water or fruit juice. If you forget and miss a dose, take it as soon as possible but never take two doses at the same time.


Laxatives such as magnesium oxide are foods, compounds or drugs that are taken to induce bowel movements or loosen the stool to relieve constipation. They act in the large intestine and colon to promote the elimination of undigested food. Excessive dosages will cause diarrhoea. This is of concern because laxatives can cause dehydration due to the large amount of water removed from the body. They also cause electrolyte imbalances as the diarrhoea drains the body of electrolytes dissolved in the water.


This laxative medication has an unpleasant taste. Take it with fruit juice or a carbonated drink. If you notice severe cramping or diarrhoea, contact your doctor. Other side-effects include hives, rashes and itching; mood changes; vertigo or dizziness; weakness and fatigue; and vomiting and nausea. Keep magnesium oxide in its original container and store it at room temperature. Do not store it in the bathroom where moisture might contaminate it. Keep it away from children and pets.

Laxative Abuse

Used in excess, magnesium oxide or any other laxative may lead to chronic constipation. Such laxative abuse can also cause intestinal paralysis, irritable bowel syndrome (IBS), renal or kidney failure and pancreatitis. The excessive use of stimulant laxatives can overstimulate the colon so that it does not readily expel faeces and constipation results.

Reactions With Other Medications

The magnesium in magnesium oxide can interfere with other medications. It decreases the absorption of digoxin and other heart medications as well as many antibiotics, including tetracycline. Magnesium oxide also interferes with some tranquillisers, antimalarial drugs and the bisphonate class of drugs, which are used to treat osteoporosis. These interactions decrease the potency of magnesium oxide as well as the other medications involved. Patients should take magnesium oxide at least two hours after the ingestion of other medications.

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