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 mild base used to neutralize stomach acid and relieve constipation. Also known as Mg(OH)₂, it’s one of the oldest and most straightforward remedies for heartburn and occasional constipation. Unlike stronger antacids, it doesn’t mask symptoms—it actually reduces acid in your stomach by reacting with it to form water and salt. That’s why it works fast, usually within 30 minutes to an hour.

But magnesium hydroxide isn’t just for heartburn. It’s also a gentle laxative, a substance that draws water into the intestines to soften stool and trigger bowel movements. That’s why it’s often found in OTC constipation relief products. People use it when they need a predictable, non-habit-forming push—especially those who can’t take stimulant laxatives. But here’s the catch: too much can lead to diarrhea, cramps, or even electrolyte imbalances. It’s not safe for long-term daily use unless a doctor says so.

It’s also worth knowing that magnesium hydroxide can interfere with how your body absorbs other medicines. If you take antibiotics like tetracycline or thyroid meds like levothyroxine, taking magnesium hydroxide at the same time can make them less effective. That’s why it’s best to space them out by at least two hours. And if you have kidney problems, your body might not flush out the extra magnesium properly, which can become dangerous over time.

Some people take it as a magnesium supplement, a source of the mineral essential for muscle function, nerve signaling, and blood sugar control. But it’s not the best form for long-term magnesium replacement—absorption is low, and it’s more likely to cause loose stools than fix a deficiency. Better options exist for that, like magnesium glycinate or citrate.

You’ll find magnesium hydroxide in dozens of over-the-counter products, often mixed with aluminum hydroxide to balance its effects. It’s in many generic brands, and even some name-brand antacids. But it’s not for everyone. Pregnant women, older adults, and those on diuretics or heart meds should check with a pharmacist first. And if you’re using it every day for more than a week, you’re probably treating a symptom, not the cause.

What you’ll find in the posts below are real, practical guides about how medications interact, how to spot hidden risks, and how to use common remedies safely. You’ll see how antacids like magnesium hydroxide fit into bigger pictures—like drug interactions, long-term use, and patient safety. Whether you’re managing occasional heartburn or helping someone else navigate their meds, these posts give you the tools to ask the right questions and avoid common mistakes.