What Is Milk of Magnesia, and What Does It Do?

Medically Reviewed By Amy Richter, RD
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Milk of magnesia, which has been around as a remedy for almost 150 years, is a common over-the-counter treatment for constipation and acid indigestion. It gets its name from the milky look of the main ingredient, magnesium hydroxide, when it is mixed with water. This article discusses what milk of magnesia is, including what it can treat. It also covers tips for taking milk of magnesia and explores the potential side effects and risks.

What is milk of magnesia?

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Milk of magnesia is made from magnesium hydroxide, which is a chemical compound present in a naturally occurring mineral called brucite. It is considered a saline laxative, which means it contains salts that draw water into the intestine.

Milk of magnesia is an alkaline mineral, which means it can neutralize stomach acid. It is meant for occasional, short-term use to help with certain digestive problems.

Uses and effects

Some of the most common uses of milk of magnesia include the following.

Constipation

The magnesium hydroxide in milk of magnesia draws water into your intestines, which softens the stool and increases pressure on the intestines. This can stimulate the bowel and make it easier to have a bowel movement. After taking milk of magnesia, people generally have a bowel movement within 30 minutes to 6 hours.

Other digestive issues

As a remedy for indigestion or heartburn, milk of magnesia’s alkaline nature neutralizes excess stomach acid and reduces burning feelings in the chest or throat, stomach cramping, and bloating.

If constipation or other symptoms do not go away within a week, call your primary care doctor or another healthcare professional.

Skin care

Some people use milk of magnesia as a home remedy for acne, oily skin, dandruff, and itchy scalp. Others use it as a makeup primer to absorb oil on the face before applying foundation.

Although there is no scientific evidence to support the claims of milk of magnesia helping with skin conditions, it continues to be a popular folk remedy.

How to take milk of magnesia

How you take milk of magnesia depends on the form of the medication you use and your symptoms. Always follow on-package instructions or speak with your pharmacist or primary care physician when taking any medication.

Types

Milk of magnesia is available as:

  • a regular-strength liquid
  • a concentrated liquid
  • chewable tablets

The dosage for the concentrated liquid is lower than that of the regular-strength liquid.

After taking the medication, drink a full 8-ounce glass of water.

Dosage

How much milk of magnesia you should take and when you should take it vary according to what form you are taking and why.

The liquid forms come with a dosing cap that shows milliliters (ml), which you should use. Do not use a household spoon, or you may take an incorrect dosage.

When taking milk of magnesia in liquid form, or as an oral suspension, you need to shake the bottle before you pour the medication.

Dosages for different digestive issues are as follows.

Constipation

  • regular-strength liquid: 30–60 ml for people over 12 years
  • concentrated liquid: 15–30 ml for people over 12 years

Milk of magnesia is also available as a chewable tablet. Follow on-package directions or talk with your doctor about proper dosing.

People often take milk of magnesia at bedtime for constipation, but it is also possible to take it at intervals during the day.

Heartburn and indigestion

  • regular-strength liquid: 5–15 ml
  • concentrated liquid: 5 ml

Always follow the directions on the package or take as directed by your doctor. Generally, do not take more than 60 ml in a 24-hour period. Do not take more than the recommended amount.

Side effects and risks

Most people tolerate milk of magnesia well, but it can cause certain side effects, including:

Using milk of magnesia too often can cause:

In rare cases, someone can take so much milk of magnesia that they develop magnesium hydroxide poisoning. This can result in the following symptoms:

If you are taking a prescription medication, ask your doctor if you can take milk of magnesia. This is important to do because it can interact with other drugs, sometimes dangerously.

People with chronic kidney disease should avoid taking too much milk of magnesia.

If you are vomiting or have stomach pain, do not take milk of magnesia without first speaking with your doctor.

If you are pregnant or breastfeeding, always check with your doctor before taking milk of magnesia. That said, it is generally considered safe to take occasionally.

When using milk of magnesia as an antacid, it may still act as a laxative. Do not use milk of magnesia as an antacid for more than 14 days in a row.

Frequently asked questions

Some other questions that people ask about milk of magnesia include the following.

Why is milk of magnesia banned?

The European Union banned milk of magnesia in 2013 due to sulfate levels in the product. However, officials allowed existing inventory to be sold.

Is milk of magnesia a strong laxative?

Milk of magnesia is considered a mild laxative when taken as directed.

Why can’t I poop even after laxatives?

Doctors define constipation as three or fewer bowel movements per week. If you do not have a bowel movement for longer than a week, even after taking a laxative, call your doctor. There can be many reasons you have difficulty moving your bowels, and a doctor can help determine the cause and recommend treatment.

Should I take milk of magnesia on an empty stomach?

Label instructions do not specify whether you should take milk of magnesia on an empty or a full stomach. However, experts recommend taking milk of magnesia at bedtime.

Summary

Milk of magnesia, which is made from a naturally occurring mineral, can be effective as a mild laxative to relieve constipation or acid indigestion.

Taken as directed, it is generally safe. However, if you take a medication or have kidney disease, talk with your doctor before using milk of magnesia.

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Medical Reviewer: Amy Richter, RD
Last Review Date: 2022 Mar 8
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THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.