Generic Name: magnesium hydroxide

Other Names: Milk of Magnesia

Drug Class: Laxatives, Other

What is magnesium hydroxide, and what is it used for?

Magnesium hydroxide, also known as milk of magnesia, is used to relieve occasional constipation and to treat heartburn and acid indigestion.

Magnesium hydroxide works as an antacid in the stomach, neutralizing the acid, and as a laxative in the colon, promoting bowel movement. Magnesium hydroxide is available over the counter in the U.S. as a generic drug.

Magnesium hydroxide is an alkaline substance that reacts with the hydrochloric acid in the stomach forming magnesium chloride and water, and increasing the pH levels in the stomach. Magnesium hydroxide is an osmotic laxative that draws water into the intestinal tract, which softens the stools and promotes peristalsis, the series of intestinal muscle contractions that enable bowel movement.

Warnings

  • Do not take magnesium hydroxide if you have any of the following conditions:
  • Use magnesium hydroxide with extreme caution in patients with:
  • Some magnesium hydroxide formulations may contain propylene glycol, which can be toxic in large quantities. Use with caution.
  • Magnesium hydroxide should be taken at least 2 hours before taking other medications, it can change the rate of absorption of other oral drugs administered concurrently.

What are the side effects of magnesium hydroxide?

Common side effects of magnesium hydroxide include:

This is not a complete list of all side effects or adverse reactions that may occur from the use of this drug.

Call your doctor for medical advice about serious side effects or adverse reactions. You may also report side effects or health problems to the FDA at 1-800-FDA-1088.

Seek medical care or call 911 at once if you have the following serious side effects while using this drug:

What are the dosages of magnesium hydroxide?

Chewable Tablet

  • 311 mg
  • 400 mg

Suspension

  • 7.75%
  • 400 mg/5mL
  • 800 mg/5mL
  • 1200 mg/15mL
  • 2400 mg/10mL

Adult:

Constipation

Suspension

  • Magnesium hydroxide (400 mg/5 mL): 30-60 mL/day orally at bedtime or in divided doses
  • Magnesium hydroxide (800 mg/5 mL): 15-30 mL/day orally at bedtime or in divided doses

Chewable tablet

  • 8 tablets/day orally at bedtime or in divided doses

Acid Indigestion

Suspension

  • Magnesium hydroxide (400 mg/5 mL): 5-15 mL orally every 4 hours; no more than 4 doses per 24-hour period

Chewable tablet

  • 2-4 tablets orally every 4 hours; no more than 4 doses per 24-hour period

Pediatric:

Constipation

  • Children younger than 2 years: Safety and efficacy not established

Suspension

  • Children 2-6 years: 5-15 mL/day of regular-strength liquid orally at bedtime or in divided doses
  • Children 6-12 years: 15-30 mL/day (400 mg/5 mL) or 7.5-15 mL/day (800 mg/5 mL) orally at bedtime or in divided doses
  • Children 12 years and older: 30-60 mL/day (400 mg/5 mL) or 15-30 mL/day (800 mg/5 mL) orally at bedtime or in divided doses

Chewable tablet

  • Children younger than 3 years: Not recommended
  • Children 3-6 years: 2 tablets orally once daily or in divided doses
  • Children 6-12 years: 4 tablets orally once daily or in divided doses
  • Children 12 years and older: 8 tablets orally once daily or in divided doses

Acid Indigestion

Suspension

  • Children younger than 12 years: Not recommended
  • Children 12 years and older: 5-15 mL (400 mg/5 mL) orally every 4 hours; no more than 4 doses per 24-hour period

Chewable tablet

  • Children younger than 12 years: Not recommended
  • Children 12 years and older: 2-4 tablets orally every 4 hours; no more than 4 doses per 24-hour period

SLIDESHOW

Super Tips to Boost Digestive Health: Bloating, Constipation, and More See Slideshow

Overdose

  • Magnesium hydroxide overdose can cause abdominal cramping, nausea and watery diarrhea. Severe overdose can raise blood levels of magnesium (hypermagnesemia) that can cause symptoms including vomiting, flushing, thirst, hypotension, drowsiness, confusion, loss of tendon reflexes, muscle weakness, respiratory depression, irregular heart rhythms (cardiac arrhythmias), coma and cardiac arrest.
  • Magnesium hydroxide overdose is treated with discontinuation of the drug, and supportive and symptomatic care as needed.

 

What drugs interact with magnesium hydroxide?

Inform your doctor of all medications you are currently taking, who can advise you on any possible drug interactions. Never begin taking, suddenly discontinue, or change the dosage of any medication without your doctor’s recommendation.

Magnesium hydroxide has no known severe interactions with other drugs.

The drug interactions listed above are not all of the possible interactions or adverse effects. For more information on drug interactions, visit the RxList Drug Interaction Checker.

It is important to always tell your doctor, pharmacist, or health care provider of all prescription and over-the-counter medications you use, as well as the dosage for each, and keep a list of the information. Check with your doctor or health care provider if you have any questions about the medication.

Pregnancy and breastfeeding

  • Occasional use of magnesium hydroxide in recommended doses during pregnancy and breastfeeding is generally considered safe.
  • Breastfeeding infants should be monitored for side effects.

What else should I know about magnesium hydroxide?

  • Take magnesium hydroxide exactly as per the package instructions.
  • Do not take magnesium hydroxide for regular bowel movement; use only for occasional constipation. Prolonged use of laxatives can cause dependence and serious side effects.
    • Bowel movement typically occurs in 30 minutes to 6 hours after taking magnesium hydroxide. Discontinue and consult your health provider if:
    • Bowel movement does not occur after use for one week
    • Rectal bleeding develops
    • Acidity symptoms don’t resolve after taking as an antacid for 2 weeks
  • Check with your physician before taking OTC magnesium hydroxide if you:
  • Keep out of reach of children.
  • In case of overdose, seek medical help or contact Poison Control.

Summary

Magnesium hydroxide, also known as milk of magnesia, is used to relieve occasional constipation and to treat heartburn and acid indigestion. Common side effects of magnesium hydroxide include diarrhea, abdominal pain, bloody stools, rectal bleeding, dehydration symptoms (dry mouth, extreme thirst, reduced urination, dizziness, electrolyte imbalance), and high magnesium in blood (hypermagnesemia). Occasional use of magnesium hydroxide in recommended doses during pregnancy and breastfeeding is generally considered safe.

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Medically Reviewed on 6/27/2022
References
REFERENCES:

https://www.rxlist.com/consumer_milk_of_magnesia_magnesium_hydroxide/drugs-condition.htm

https://reference.medscape.com/drug/milk-of-magnesia-magnesium-hydroxide-342018#0

https://www.uptodate.com/contents/magnesium-hydroxide-drug-information

https://www.webmd.com/drugs/2/drug-8802/magnesium-hydroxide-oral/details

https://go.drugbank.com/drugs/DB09104