Magnesium Hydroxide


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.

Side Effects Of Magnesium Hydroxide

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.

Warnings & Precautions

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 this medication, call your doctor.

Dosage Of Magnesium Hydroxide

Magnesium hydroxide comes 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 it 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 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 this medication for longer than 1 week without talking to your doctor.

Shake the oral suspension well before each use.


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.


All information has been provided courtesy of MedLinePlus from the National Library of Medicine and from the FDA.