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Magnesium Hydroxide

pronounced as (mag nee' zee um) (hye drox' ide)

Why is this medication prescribed?

Magnesium hydroxide is used to treat occasional constipation in children and adults on a short-term basis. Magnesium hydroxide is in a class of medications called saline laxatives. It works by causing water to be retained with the stool. This increases the number of bowel movements and softens the stool so it is easier to pass.

How should this medicine be used?

Magnesium hydroxide come as a chewable tablet, tablet, and a suspension (liquid) to take by mouth. It usually is taken as a single daily dose (preferably at bedtime) or you may divide the dose into two or more parts over one day. Magnesium hydroxide usually causes a bowel movement within 30 minutes to 6 hours after taking it. Follow the directions on the package or on your product label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take magnesium hydroxide exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.

If you are giving magnesium hydroxide to your child, read the package label carefully to make sure that it is the right product for the age of the child. Do not give children magnesium hydroxide products that are made for adults. Check the package label to find out how much medication the child needs. Ask your child's doctor if you don't know how much medication to give your child.

Take the suspension, chewable tablets, and tablets with a full glass (8 ounces [240 milliliters]) of liquid.

Do not take magnesium hydroxide for longer than 1 week without talking to your doctor.

Shake the oral suspension well before each use.

Other uses for this medicine

Magnesium hydroxide is also used as an antacid with other medications to relieve heartburn, acid indigestion, and upset stomach.

This medication may be prescribed for other uses; ask your doctor or pharmacist for more information.

What special precautions should I follow?

Before taking magnesium hydroxide,

  • tell your doctor and pharmacist if you are allergic to magnesium hydroxide, any other medications, or any of the ingredients in magnesium hydroxide preparations. Ask your pharmacist or check the product label for a list of the ingredients.
  • tell your doctor and pharmacist what other prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Your doctor may need to change the doses of your medications or monitor you carefully for side effects.
  • if you are taking other medications, take them at least 2 hours before or 2 hours after taking magnesium hydroxide.
  • tell your doctor if you have stomach pain, nausea, vomiting, or a sudden change of bowel habits lasting more than 2 weeks. Also, tell your doctor if you have or have ever had kidney disease.
  • tell your doctor if you are pregnant, plan to become pregnant, or are breastfeeding. If you become pregnant while taking magnesium hydroxide, call your doctor.

What should I do if I forget a dose?

Tell your doctor if you are on a magnesium-restricted diet before taking magnesium hydroxide. Unless your doctor tells you otherwise, continue your normal diet.

What side effects can this medication cause?

Magnesium hydroxide may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:

  • loose, watery, or more frequent stools

Some side effects can be serious. If you experience any of these symptoms, stop taking magnesium hydroxide and call your doctor immediately:

  • blood in stool
  • unable to have a bowel movement 6 hours after use

Magnesium hydroxide may cause other side effects. Call your doctor if you have any unusual problems while taking this medication.

If you experience a serious side effect, you or your doctor may send a report to the Food and Drug Administration's (FDA) MedWatch Adverse Event Reporting program online ( or by phone (1-800-332-1088).

What should I know about storage and disposal of this medication?

Keep this medication in the container it came in, tightly closed, and out of reach of children. Store it at room temperature and away from excess heat and moisture (not in the bathroom). Do not freeze the suspension.

It is important to keep all medication out of sight and reach of children as many containers (such as weekly pill minders and those for eye drops, creams, patches, and inhalers) are not child-resistant and young children can open them easily. To protect young children from poisoning, always lock safety caps and immediately place the medication in a safe location – one that is up and away and out of their sight and reach.

Unneeded medications should be disposed of in special ways to ensure that pets, children, and other people cannot consume them. However, you should not flush this medication down the toilet. Instead, the best way to dispose of your medication is through a medicine take-back program. Talk to your pharmacist or contact your local garbage/recycling department to learn about take-back programs in your community. See the FDA's Safe Disposal of Medicines website ( for more information if you do not have access to a take-back program.

What other information should I know?

Ask your pharmacist any questions you have about magnesium hydroxide.

It is important for you to keep a written list of all of the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.

Brand names

  • Milk of Magnesia®
  • Pedia-Lax®
  • Almacone® (containing Aluminum Hydroxide, Magnesium Hydroxide, Simethicone)
  • Alumox® (containing Aluminum Hydroxide, Magnesium Hydroxide, Simethicone)
  • ConRX® AR (containing Aluminum Hydroxide, Magnesium Hydroxide)
  • Duo Fusion® (containing Calcium Carbonate, Famotidine, Magnesium Hydroxide)
Last Revised - 04/15/2019