Magnesium Hydroxide (Milk of Magnesia): What It Does and How to Use It

Magnesium hydroxide, commonly called Milk of Magnesia, is an over-the-counter antacid and laxative. People grab it for quick heartburn relief or to relieve occasional constipation. It works two ways: it neutralizes stomach acid for fast heartburn relief and draws water into the bowel to soften stools and speed their passage.

Before using it, read the label and pick the right product — some formulas are stronger or flavored for kids. If you’re unsure, talk to a pharmacist or your doctor, especially when other health issues or medicines are involved.

How to take it and what to expect

For heartburn or sour stomach, small doses after meals and at bedtime usually ease symptoms in minutes. For constipation, a larger dose (often taken at bedtime) can produce a bowel movement in a few hours to overnight. Timing depends on the exact product and dose, so follow the package directions.

Adults: follow the product label—many liquid suspensions suggest a small antacid dose after meals and a larger laxative dose at night. Children: use a pediatric formulation and follow the age/weight dosing or check with your pediatrician.

Safety tips, side effects, and drug interactions

Common side effects are mild: diarrhea, cramping, and sometimes nausea. Diarrhea is more likely with higher doses. Stop use if you get severe stomach pain, continuous diarrhea, or signs of dehydration.

If you have kidney disease, don’t take magnesium hydroxide without medical advice. Kidneys clear excess magnesium; impaired function can cause magnesium to build up. Signs of high magnesium (hypermagnesemia) include very low blood pressure, extreme drowsiness, muscle weakness, and breathing trouble—seek urgent care if these appear.

Magnesium hydroxide can reduce absorption of some medicines like certain antibiotics (tetracyclines, fluoroquinolones) and thyroid meds. To avoid this, take those drugs at least two hours before or after magnesium hydroxide.

Long-term laxative use can make your bowel depend on laxatives and hide underlying problems. If constipation lasts more than two weeks or keeps coming back, see your doctor. Try simple fixes first: more fiber, water, and regular activity.

Store the suspension at room temperature, keep it tightly closed, and shake well before use. If the product smells off or changes color, toss it.

If you’re pregnant or breastfeeding, check with your healthcare provider. Short-term use is often safe, but your provider can recommend the best option for you.

Want alternatives? For mild heartburn, antacids like calcium carbonate work well. For constipation, bulk-forming fiber or stool softeners may be gentler for long-term use. Ask your pharmacist which choice fits your situation.

Use magnesium hydroxide for occasional relief and follow dosing instructions. When in doubt—especially with chronic symptoms, kidney disease, or multiple medications—get professional advice.