Magnesium Hydroxide: What It Is and Why You Might Need It

Magnesium hydroxide shows up on pharmacy shelves as Milk of Magnesia. Most people know it as a heartburn reliever or a gentle laxative, but the details matter. It’s a simple salt that can neutralize stomach acid and draw water into the colon, helping things move along. If you’re wondering when to reach for it, how much to take, or what to watch out for, this guide breaks it down in plain English.

How Magnesium Hydroxide Works

When you swallow magnesium hydroxide, it reacts with the acid in your stomach to form magnesium chloride and water. The result is less acid, which eases the burning feeling of heartburn. At the same time, the compound stays mostly unchanged until it reaches your large intestine. There, it pulls water into the bowel, softening stool and prompting a smoother bowel movement. Because it does two jobs, you’ll often see it marketed for both relief of indigestion and occasional constipation.

When to Use and How to Take It

Use magnesium hydroxide for short‑term heartburn or mild constipation. It’s not meant for chronic conditions without a doctor’s okay. For heartburn, the usual adult dose is 1½ to 2 teaspoons (≈7.5‑10 mL) of the liquid after meals. For constipation, adults often start with 2 to 4 teaspoons (≈15‑30 mL) at bedtime, but you can adjust based on how you feel. Always read the label – some brands are more concentrated than others.

Take the liquid with a full glass of water. If you prefer pills, the same principles apply: follow the number of tablets listed on the package, typically 2‑4 tablets for constipation. Kids need much smaller doses, and you should check a pediatric dosing chart or ask a pharmacist.

Don’t mix magnesium hydroxide with other antacids unless a health professional tells you it’s okay. Combining them can lead to too little stomach acid, which might affect digestion of certain nutrients.

Watch for side effects. The most common are loose stools or a mild, chalky taste in the mouth. If diarrhea lasts more than two days, stop using it and talk to a doctor. Rarely, people develop high magnesium levels – symptoms include muscle weakness, low blood pressure, or irregular heartbeat. This is mostly a risk for people with kidney problems, so they should avoid over‑the‑counter magnesium hydroxide unless cleared by a clinician.

Magnesium hydroxide can interact with some prescription meds. It may reduce the absorption of antibiotics like tetracycline or fluoroquinolones, and it can affect heart medications such as digoxin. Space out doses by at least two hours if you’re on any of these drugs.

What about alternatives? If you need an antacid but want something without a laxative effect, calcium carbonate (Tums) works well for occasional heartburn. For constipation, fiber supplements, stool softeners like docusate, or a higher‑dose magnesium citrate can be gentler on the gut. Choose based on whether acid relief or bowel regulation is your main goal.

Store magnesium hydroxide in a cool, dry place, away from direct sunlight. Once opened, keep the bottle tightly sealed to avoid contamination.

Bottom line: magnesium hydroxide is a handy, low‑cost option for occasional heartburn and constipation, but it’s best used short term and at the recommended dose. If your symptoms linger, it’s time to see a doctor rather than keep reaching for the bottle.