Magnesium Hydroxide (Milk of Magnesia): Uses, Dosing & Safety
If you’ve bought Milk of Magnesia for a stubborn bout of constipation or heartburn, you’ve already met magnesium hydroxide. It’s a common over-the-counter drug that works two ways: it neutralizes stomach acid as an antacid and pulls water into the bowel as an osmotic laxative. That dual action makes it handy, but it also means you should use it the right way.
How it works and when to use it
As an antacid, magnesium hydroxide neutralizes excess stomach acid and can give quick relief from indigestion or mild heartburn. As a laxative, it draws water into the intestines, softening stool and stimulating bowel movements. People use it for occasional constipation, to clean out the bowel before some tests, or for short-term relief of gastric acidity.
Use it when constipation is occasional (not chronic). If you need a laxative more than once a week, talk to a healthcare provider—long-term use can hide other problems or create dependence.
Practical dosing and tips
Liquid Milk of Magnesia is the usual OTC form. Adults commonly take 15–30 ml (1–2 tablespoons) as a single dose for constipation; follow the product label. For heartburn, smaller doses may be used—check the package. Children’s doses depend on age and weight, so follow pediatric instructions or ask your pharmacist. Don’t mix it with other oral medicines at the same time—magnesium can bind some drugs and make them less effective. A safe rule: separate other meds by at least 2 hours.
Give it with a full glass of water and expect results in a few hours to a day for constipation. If you don’t see improvement or symptoms return quickly, stop and consult a clinician.
Common side effects are loose stools, abdominal cramping, and occasional nausea. These usually clear up after stopping the medicine. Serious problems are rare but can happen—watch for severe diarrhea, signs of dehydration, or muscle weakness. Those can indicate an electrolyte imbalance or excess magnesium.
People with kidney disease should be cautious. Kidneys clear magnesium; if they don’t work well, magnesium can build up and cause toxicity. Also avoid or check with your doctor if you take certain antibiotics (like tetracyclines or quinolones), bisphosphonates, or levothyroxine—magnesium can lower how well those drugs work.
Pregnant or breastfeeding? Magnesium hydroxide is sometimes used in pregnancy for constipation, but check with your provider first. For infants and very young children, follow pediatric advice closely—do not give adult doses.
Store the bottle tightly closed at room temperature and keep it out of reach of children. If you see bloody stools, severe belly pain, high fever, or no bowel movement after using a laxative, seek medical help right away.
At Canadian-Tabls Health Portal we collect clear, practical guides like this so you can understand common medicines without the jargon. Use this info to ask smart questions at the pharmacy or doctor’s office. If you’re unsure about dosing or interactions, call your healthcare provider before taking magnesium hydroxide.
