Magnesium Hydroxide: Uses, Side Effects, and What You Need to Know

When you reach for a bottle of milk of magnesia, you’re using magnesium hydroxide, a simple compound used for decades to relieve heartburn and constipation. Also known as Mg(OH)₂, it’s one of the most straightforward drugs on the shelf—no fancy delivery system, no complex dosing. Just a white suspension that works fast and cheap. But don’t let its simplicity fool you. This isn’t just a quick fix. Used wrong, it can throw off your electrolytes, mess with kidney function, or hide a deeper problem like chronic constipation or acid reflux.

Magnesium hydroxide works in two ways: as an antacid, it neutralizes stomach acid by reacting with hydrochloric acid to form salt and water, and as a laxative, it pulls water into the intestines to soften stool and trigger movement. That’s why it shows up in products for heartburn, indigestion, and occasional constipation. But if you’re taking it daily, you’re not treating the cause—you’re masking it. Long-term use can lead to dependence, where your bowels stop working unless you’ve had a dose. And if you have kidney issues, magnesium can build up in your blood, causing nausea, low blood pressure, or worse.

People often mix it up with other magnesium forms—like magnesium citrate or oxide—but they’re not the same. Magnesium hydroxide is slower to absorb, which is why it’s better for constipation than for boosting magnesium levels in the body. It’s also less likely to cause diarrhea than citrate, unless you take too much. And while it’s safe for short-term use, it’s not a substitute for dietary changes, fiber, or proper hydration. If you’re relying on it every week, talk to your doctor. There might be a better, safer way.

What you’ll find below are real stories and science-backed insights about magnesium hydroxide—from how it interacts with other meds, to why some people swear by it while others get sick from it, to when it’s time to stop using it altogether. These aren’t generic advice posts. They’re practical, no-fluff guides from people who’ve been there and checked the data.