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Magnesium hydroxide

Brand names: Milk of Magnesia, Phillips'

Magnesium hydroxide (milk of magnesia) relieves constipation and, in small amounts, heartburn.

Brand namesMilk of Magnesia, Phillips'
Type of medicineOsmotic laxative and antacid
Prescription?Over the counter
ImportantThis page is general information, not a prescription. Don't start, stop, or change a medicine without talking to your provider or pharmacist.

Overview

It usually works in 30 minutes to 6 hours.

What it's used for

  • Occasional constipation
  • Heartburn and acid indigestion

How to take it

  • Shake well and follow the label. Take with a full glass of water for constipation.

Your dose depends on your health and other medicines. Always follow your prescription label, and ask your pharmacist if anything is unclear.

Side effects

Common side effects

  • Diarrhea
  • Cramps
Call your provider todayWeakness, slow breathing, or confusion (too much magnesium, mainly with kidney disease)

Warnings

  • Ask a provider first if you have kidney disease.

Other medicines, foods, and alcohol

  • It lowers absorption of many medicines, including some antibiotics and levothyroxine; separate by 2 hours.

Tell your provider and pharmacist about every medicine, vitamin, and supplement you take.

Pregnancy and breastfeeding

Ask your provider.

Missed doses, overdose, and storage

If you miss a dose

This medicine is often taken only when needed. If you take it on a schedule, take a missed dose when you remember, unless it's almost time for the next one. Don't double up.

If someone takes too much

Call Poison Control at 1-800-222-1222 or get help online at poison.org. Call 911 if the person collapses, has a seizure, has trouble breathing, or can't be woken.

Storing it

Store at room temperature, away from heat and moisture (not in the bathroom), and out of reach of children and pets.

Conditions it's used for

Sources

Last updated 2026-11-13.