magnesium hydroxide

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.

• Do not take magnesium hydroxide if you have any of the following conditions:
  • Preexisting electrolyte imbalance
  • Undiagnosed abdominal pain
  • Fecal impaction
  • Rectal fissures
  • Intestinal obstruction or perforation
  • Any acute abdominal condition requiring surgery (acute surgical abdomen) including appendicitis
  • Heart block or damage to the heart muscle (myocardial damage)
  • Kidney failure
• Use magnesium hydroxide with extreme caution in patients with:
  • Impaired kidney function
  • Neuromuscular diseases such as myasthenia gravis
• 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.

Common side effects of magnesium hydroxide include:

• Diarrhea
• Abdominal pain
• Bloody stools
• Rectal bleeding
• Dehydration symptoms such as:
  • Dry mouth
  • Extreme thirst
  • Reduced urination
  • Dizziness
• Electrolyte imbalance
• High magnesium in blood (hypermagnesemia) with symptoms including:
  • Low blood pressure (hypotension)
  • Muscle weakness
  • Slow and shallow breathing (respiratory depression)
  • Irregular heart rhythm (cardiac arrhythmia)
  • Confusion

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:

• Serious heart symptoms such as fast, irregular, or pounding heartbeats; fluttering in your chest; shortness of breath; and sudden dizziness, lightheartedness, or passing out;
• Severe headache, confusion, slurred speech, arm or leg weakness, trouble walking, loss of coordination, feeling unsteady, very stiff muscles, high fever, profuse sweating, or tremors;
• Serious eye symptoms such as sudden vision loss, blurred vision, tunnel vision, eye pain or swelling, or seeing halos around lights.

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

• 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.

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.

• Serious interactions of magnesium hydroxide include:
  • baloxavir marboxil
  • demeclocycline
  • doxycycline
  • eltrombopag
  • infigratinib
  • minocycline
  • oxytetracycline
  • pazopanib
  • ponatinib
  • potassium phosphates, IV
  • raltegravir
  • sotorasib
  • tetracycline
• Moderate interactions of magnesium hydroxide include:
  • bictegravir
  • cabotegravir
  • chloroquine
  • ciprofloxacin
  • deferiprone
  • deflazacort
  • dolutegravir
  • fleroxacin
  • gemifloxacin
  • levofloxacin
  • moxifloxacin
  • ofloxacin
  • omadacycline
  • sodium phosphates, IV
  • vismodegib
  • vitamin D
• Magnesium Hydroxide has mild interactions with at least 42 different 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.

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

• 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:
  • Have kidney dysfunction
  • Are on magnesium-restricted diet
  • Have nausea, vomiting and/or abdominal pain
  • Sudden change in bowel habits persisting over 2 weeks
• Keep out of reach of children.
• In case of overdose, seek medical help or contact Poison Control.