Magnesium Hydroxide

Magnesium hydroxide is an antacid that neutralizes stomach acid and promotes bowel movement as a laxative. It is available over the counter in the U.S. as a generic drug.

This alkaline substance reacts with hydrochloric acid in the stomach, increasing pH levels and forming magnesium chloride and water. As an osmotic laxative, it draws water into the intestines, softening stools and promoting peristalsis, the contraction of intestinal muscles necessary for bowel movement.

Warnings

• Do not use magnesium hydroxide if you have:

• Electrolyte imbalance
• Undiagnosed abdominal pain
• Fecal impaction
• Rectal fissures
• Intestinal obstruction or perforation
• Condition requiring abdominal surgery
• Heart block or myocardial damage
• Kidney failure
• Impaired kidney function
• Certain neuromuscular diseases

Side Effects

Common side effects of magnesium hydroxide include:

• Diarrhea
• Abdominal pain
• Bloody stools
• Rectal bleeding
• Dehydration symptoms such as dry mouth, extreme thirst, reduced urination, and dizziness
• Low blood pressure, muscle weakness, slow and shallow breathing, and irregular heart rhythm
• Confusion

This is not a complete list of side effects. Contact your doctor or report any serious side effects or adverse reactions to the FDA.

Seek immediate medical care or call 911 if you experience the following serious side effects:

• Fast, irregular, or pounding heartbeats
• Slurred speech, weakness, coordination problems, high fever, or tremors
• Vision loss, eye pain, or swelling

Dosages

Chewable Tablet

Suspension

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

Adult:

• 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
• 8 tablets/day orally at bedtime or in divided doses
• Magnesium hydroxide (400 mg/5 mL): 5-15 mL orally every 4 hours; no more than 4 doses per 24-hour period
• 2-4 tablets orally every 4 hours; no more than 4 doses per 24-hour period

Pediatric:

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

Question

Overdose

• Magnesium hydroxide overdose can cause abdominal cramping, nausea, and watery diarrhea. Severe overdose can result in high blood magnesium levels (hypermagnesemia) and symptoms such as vomiting, flushing, thirst, low blood pressure, drowsiness, confusion, loss of reflexes, muscle weakness, respiratory depression, irregular heart rhythms, coma, and cardiac arrest.
• Discontinue the drug and seek supportive and symptomatic care if an overdose occurs.

Drug Interactions

Inform your doctor of all medications you are taking to check for possible drug interactions. Do not start, stop, or change medication without medical advice.

Magnesium hydroxide has no known severe interactions with other drugs. However, it can interact with certain medications. Consult the RxList Drug Interaction Checker for more information.

Tell your healthcare provider about all prescription and over-the-counter medications you use.

Pregnancy and Breastfeeding

• Occasional use of magnesium hydroxide in recommended doses during pregnancy and breastfeeding is generally safe.
• Monitor breastfed infants for side effects.

Additional Information

• Follow the package instructions for magnesium hydroxide.
• Use it only for occasional constipation, not for regular bowel movement. Prolonged use can cause dependence and serious side effects.
• Consult your healthcare provider if:

• Bowel movement does not occur after one week of use
• Rectal bleeding develops
• Acidity symptoms persist after two weeks of use
• You have kidney dysfunction or are on a magnesium-restricted diet
• You experience nausea, vomiting, or abdominal pain
• You have sudden changes in bowel habits persisting for over two weeks

Summary

Magnesium hydroxide, also known as milk of magnesia, relieves occasional constipation, heartburn, and acid indigestion. Common side effects include diarrhea, abdominal pain, bloody stools, rectal bleeding, dehydration symptoms, and high magnesium levels. Occasional use during pregnancy and breastfeeding is generally safe.