Milk of magnesia: Uses, types, risks, and interactions

This article will explain what it is and how to use it, along with common side effects.

What is milk of magnesia?

Milk of magnesia contains magnesium, which is a naturally occurring mineral. The human body requires magnesium to help many of its systems function properly, most notably the muscles and the nerves.

Milk of magnesia is also known as magnesium hydroxide, which is its chemical name. Milk of magnesia is available to buy over the counter without a prescription.

People should not give milk of magnesia to children under 2 years of age unless advised by a doctor.

Uses and effects

People use milk of magnesia as a laxative to relieve constipation, and to ease indigestion and heartburn. This is because it can reduce the amount of stomach acid while increasing water in the intestines.

Magnesium hydroxide works by drawing water from the tissue around the bowel into the gut to ‘flush’ the contents out.

The original form of milk of magnesia usually produces a bowel movement in 30 minutes to 6 hours.

Milk of magnesia is one of the most commonly used over-the-counter treatments for constipation. Constipation is when a person is passing stools fewer than three times a week.

People experiencing constipation may report the following symptoms:

  • hard, lumpy stools
  • bloating
  • not feeling fully empty after going to the toilet
  • discomfort in the abdominal area
  • feeling the need to strain excessively

Most people who take milk of magnesia do not experience side effects.

The most common side effects of milk of magnesia are:

  • diarrhea
  • stomach cramps
  • chalky taste
  • feeling nauseous
  • vomiting

Milk of magnesia also carries more serious side effects. People who experience any of the following should stop using the medicine straight away and seek medical attention:

  • rectal bleeding
  • no bowel movement after taking it
  • severe nausea or vomiting
  • slow heartbeat
  • light-headedness

Serious side effects are more likely to occur if a person takes more milk of magnesia than is recommended, or if they take it for an extended period.

Magnesium may be able to cross the placenta into the body of the fetus. However, doctors do not know if milk of magnesia is safe for use during pregnancy as there is no data on this.

Small amounts of magnesium may also make its way into breast milk, but again, doctors do not know the safety of this.

As such, the general advice is to avoid using milk of magnesia when pregnant or breastfeeding.

Interactions

Milk of magnesia interferes with a wide range of medicines, which means it affects how they work. These include prescription and over-the-counter medicine, as well as vitamins and supplements.

Because of the way it impacts the liquids in the gut, milk of magnesia can stop tablets from being absorbed properly.

Examples of possible interactions include:

  • tetracycline
  • digoxin
  • penicillamine
  • bisphosphonates
  • ketoconazole

Summary

Milk of magnesia is a well-known and effective laxative for the short-term treatment of constipation.

People should not use milk of magnesia for more than 7 days at a time for constipation or 14 days at a time for other digestive issues. Ongoing symptoms can be a sign of a more serious gut health condition, so if the problem persists, a person should see their doctor.

Milk of magnesia works by drawing water into the bowel from the surrounding tissue. This means it can stop a range of other medications, including prescription drugs, supplements, and vitamins, from being absorbed by the body.

One of the most common causes of constipation is a low-fiber diet. Eating foods rich in fiber, such as fruit, vegetables, and whole grains can reduce a person’s chances of developing constipation.

Drinking plenty of water is also important to keep the bowels moving.

Anyone who takes medication for a health condition should talk to a doctor before taking milk of magnesia.

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