Milk of magnesia is an over-the-counter (OTC) treatment for constipation. It works by drawing water into the bowel and softening stool, making passing easier. It can also soothe indigestion and heartburn.
This article explains what milk of magnesia is, how to use it, what conditions it can treat, common side effects, and more.
Milk of magnesia, also known as magnesium hydroxide, can act as an antacid or as a saline laxative. This type of laxative works by drawing water into a person’s bowels to help loosen stool.
People use milk of magnesia for:
- constipation, because when used as a laxative, milk of magnesia draws water into the bowel to help soften and remove stool
- indigestion and heartburn
The original form of milk of magnesia usually helps a person produce a bowel movement in 30 minutes to 6 hours.
In addition to constipation and acid relief, milk of magnesia may help with conditions such as sunburn, diaper rash, and acne, though empirical evidence is significantly lacking.
Milk of magnesia can be purchased as a tablet or a liquid. When using the tablet form, a person usually needs to chew the tablet before swallowing it.
Milk of magnesia is available as a regular-strength liquid or a concentrated liquid. People should not give the concentrated liquid to children under 12.
People should not take more medication than their doctor or the packaging recommends. Though dosing can vary, a person should avoid taking more than the recommended dose over 24 hours.
The dosage varies depending on why the person is using the medication and their age.
Original milk of magnesia
People who are old enough to take milk of magnesia should drink a full glass, or 8 ounces, of water with each dose of milk of magnesia. Use the 15-milliliter (ml) dosing cup or spoon provided for accuracy. It is best to take the medication at bedtime.
Using the original version of milk of magnesia for constipation, the dosage in milliliters varies depending on a person’s age:
- Adults and children 12 or older can take 30–60 ml.
- Children ages 6–11 can take 15–30 ml.
- Ask a doctor before giving this medication to children under 6 years old.
Concentrated milk of magnesia
For the concentrated version of milk of magnesia, the dosage is lower:
- Adults can take 15–30 ml.
- Ask a doctor before giving this medication to children under 12 years old.
Milk of magnesia tablets
There are also chewable tablets for children. Children should drink a full glass of liquid with each dose. The dosage varies depending on a person’s age and medication guidance.
People should not take milk of magnesia as a laxative for more than 7 days in a row. Anyone who is still in need of a laxative or has persistent pain in their stomach area should talk with a doctor.
Milk of magnesia for other digestive issues
Along with constipation relief, people can also use some versions of milk of magnesia to relieve heartburn and acid indigestion.
Adults should take 5 to 15 ml at a time with water and repeat up to four times per day as needed. They should not take more than 60 ml in any 24-hour period.
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
- nausea
- vomiting
Milk of magnesia also carries the risk of more serious side effects. People who experience any of the following should stop using the medication and seek medical attention:
- rectal bleeding
- no bowel movement after taking it
- severe nausea or vomiting
- slow heartbeat
- lightheadedness
People who are taking this medication need to drink plenty of water to prevent dehydration. If anyone experiences diarrhea after taking a dose of milk of magnesia, they should not use it again.
Some people may be allergic to milk of magnesia. Signs of an allergic reaction that require medical attention include:
- hives
- difficulty breathing
- swelling of the face, lips, tongue, or throat
People living with impaired kidney function should avoid milk of magnesia. The following people should also avoid taking the medication:
- people on a magnesium-restricted diet
- people with symptoms such as nausea, vomiting, diarrhea, or stomach pain
- people who experience sudden bowel changes that last longer than 14 days
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.
The general advice is to avoid using milk of magnesia when pregnant or nursing or ask a doctor before use.
Because of the way it impacts the liquids in the gut, milk of magnesia can stop tablets from being absorbed properly.
As a result, a person should talk with their doctor before using milk of magnesia if they regularly take other medications, including OTC medications, vitamins, and prescription medications.
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 indicate a more serious gut health condition, so if the problem persists, a person should contact their doctor.
Milk of magnesia works by drawing water into the bowel from the surrounding tissue. This means it can stop the body from absorbing a range of other medications, including prescription drugs, supplements, and vitamins. Anyone who takes medication for a health condition should talk with a doctor before taking milk of magnesia.
