Phillips' Milk of Magnesia - National Multiple Sclerosis Society

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Phillips' Milk of Magnesia


About this Medication
  • Brand Name: Phillips' Milk of Magnesia
  • Chemical Name: magnesium hydroxide (mag-nee-zhum hye-drox-ide)
  • Usage in MS: Constipation
  • Generic Available: No

This medication is available without a prescription.


Magnesium hydroxide is an over-the-counter hyperosmotic laxative of the saline type that encourages bowel movements by drawing water into the bowel from surrounding body tissue. Saline hyperosmotic laxatives (often called "salts") are used for rapid emptying of the lower intestine and bowel. They are not to be used for the long-term management of constipation.

Proper Usage

Laxatives are to be used to provide short-term relief only, unless otherwise directed by the nurse or physician who is helping you to manage your bowel symptoms. A regimen that includes a healthy diet containing roughage (whole grain breads and cereals, bran, fruit, and green, leafy vegetables), six to eight full glasses of liquids each day, and some form of daily exercise is most important in stimulating healthy bowel function.

If your physician has recommended this laxative for management of constipation, follow his or her recommendations for its use. If you are treating yourself for constipation, follow the directions on the package insert. Results are often obtained ninety minutes to three hours after taking a hyperosmotic laxative. Be sure to consult your physician if you experience problems or do not get relief within a week.

Each dose should be taken with eight ounces or more of cold water or fruit juice. A second glass of water or juice with each dose is often recommended to prevent dehydration. If concerns about loss of bladder control keep you from drinking this amount of water, talk it over with the nurse or physician who is helping you manage your bowel and bladder symptoms.


Do not take any type of laxative if you have signs of appendicitis or inflamed bowel (e.g., stomach or lower abdominal pain, cramping, bloating, soreness, nausea or vomiting). Check with your physician as soon as possible.

Do not take any laxative for more than one week unless you have been told to do so by your physician. Many people tend to overuse laxatives, which often leads to dependence on the laxative action to produce a bowel movement. Discuss the use of laxatives with your health care professional in order to ensure that the laxative is used effectively as part of a comprehensive, healthy bowel management regimen.

Do not take any laxative within two hours of taking another medication because the desired effectiveness of the other medication may be reduced.

Although laxatives are commonly used during pregnancy, some types are better than others. If you are pregnant, consult your physician about the best laxative for you to use.

Some laxatives pass into breast milk. Although it is unlikely to cause problems for a nursing infant, be sure to let your physician know if you are using a laxative and breast-feeding at the same time.

Possible Side Effects

Side effects that may go away as your body adjusts to the medication and do not require medical attention unless they continue or are bothersome: cramping; diarrhea; gas; increased thirst.

Unusual side effects that should be reported to your physician as soon as possible: confusion; dizziness; irregular heartbeat; muscle cramps, unusual tiredness or weakness*.

*Since it may be difficult to distinguish between certain common symptoms of MS and some side effects of magnesium hydroxide, be sure to consult your health care professional if an abrupt change of this type occurs.