Milk of magnesia is a liquid laxative used to relieve occasional constipation. It works by drawing water into the intestines, which softens stool and stimulates a bowel movement. It is also used as an antacid to relieve heartburn, sour stomach, and acid indigestion. The active ingredient is magnesium hydroxide, a compound that has been used in medicine for over a century.
How Does Milk of Magnesia Work?
Milk of magnesia works through a simple osmotic effect. The magnesium hydroxide in the liquid is not easily absorbed by the intestines. Because of this, it stays in the digestive tract and pulls water from surrounding tissues into the bowels.
This extra water softens the stool and increases its volume. The stretching of the intestinal wall triggers natural muscle contractions, called peristalsis, which move the stool along and produce a bowel movement. This process typically takes anywhere from 30 minutes to six hours, depending on the form you take and your individual digestive system.
As an antacid, milk of magnesia neutralizes stomach acid directly. The magnesium hydroxide reacts with hydrochloric acid in the stomach to form magnesium chloride and water. This reaction reduces acidity and relieves the burning sensation of heartburn and indigestion.
Common Uses for Milk of Magnesia
The primary use is treating constipation. It is considered a saline laxative, meaning it uses salts to pull water into the bowels. It is a well-established option for short-term relief of constipation in adults.
The second common use is as an antacid. People take it for heartburn, acid reflux symptoms, and upset stomach. The FDA recognizes both uses as safe and effective when the product is used according to label directions.
Some people use milk of magnesia for other purposes, such as treating acne or as a deodorant. These uses are not backed by clinical evidence. No studies have confirmed that applying milk of magnesia to the skin clears acne or reduces body odor. If you hear these claims, treat them with skepticism.
What Forms Are Available?
Milk of magnesia comes in two main forms: liquid and chewable tablets. The liquid form is the most common and acts fastest. It comes in regular and concentrated versions.
Regular strength liquid typically contains 400 mg of magnesium hydroxide per 5 mL (one teaspoon). Concentrated versions contain 800 mg per 5 mL. The concentrated form requires a smaller dose and works more quickly.
Chewable tablets are also available, usually containing 311 mg of magnesium hydroxide per tablet. Tablets take longer to work than the liquid form because they must dissolve and be digested first.
You can find both flavored and unflavored versions of the liquid. The unflavored version has a chalky taste that many people find unpleasant. Flavored versions mask this with mint or citrus flavors.
How Should You Take It?
Always follow the dosing instructions on the product label. The correct dose depends on your age and the specific product you purchased. Never exceed the recommended dose.
For adults and children 12 years and older, the typical laxative dose of regular strength liquid is 30 to 60 mL. The typical antacid dose is 5 to 15 mL. For the concentrated form, the laxative dose is usually 15 to 30 mL.
For children ages 6 to 11, the typical laxative dose is 15 to 30 mL of regular strength liquid. For children ages 2 to 5, the dose is 5 to 15 mL. You should not give milk of magnesia to children under 2 years old without a doctor’s approval.
Shake the bottle well before measuring. Use the dosing cup that comes with the product, not a kitchen spoon. Kitchen spoons vary in size and can lead to incorrect dosing.
Take the liquid with a full glass of water. This helps the osmotic effect work properly. The medication works best when your body is well hydrated.
Who Should Not Take Milk of Magnesia?
Milk of magnesia is not safe for everyone. People with kidney disease should avoid it unless a doctor specifically recommends it. The kidneys normally filter excess magnesium from the blood. If your kidneys do not work well, magnesium levels can build up to dangerous levels.
People with severe abdominal pain, nausea, or vomiting should not take this medication. These symptoms can signal appendicitis or another serious condition. Taking a laxative in this situation can be harmful.
People on a low-magnesium diet for medical reasons should talk to their doctor first. Similarly, anyone with a sudden change in bowel habits lasting more than two weeks should seek medical advice before self-treating.
Pregnant women should consult their healthcare provider before using milk of magnesia. While it is generally considered low risk, no medication should be assumed safe during pregnancy without a doctor’s guidance. The same applies to breastfeeding women.
What Are the Side Effects?
Milk of magnesia is generally well tolerated when used occasionally and at correct doses. The most common side effects are diarrhea, stomach cramps, and nausea. These effects are usually mild and pass quickly.
More serious side effects can occur with overuse or in people with kidney problems. These include confusion, muscle weakness, irregular heartbeat, and a drop in blood pressure. These symptoms can indicate hypermagnesemia, a condition of too much magnesium in the blood.
Hypermagnesemia is a medical emergency. If you experience severe dizziness, difficulty breathing, or an irregular heartbeat after taking milk of magnesia, seek emergency medical care immediately.
How Long Can You Use It?
Milk of magnesia is meant for short-term use only. You should not use it as a daily laxative for more than one week without a doctor’s supervision.
Using laxatives regularly can lead to dependence. Your colon may begin to rely on the medication to produce a bowel movement. Over time, normal bowel function can weaken, and you may find it harder to go without the laxative.
If constipation lasts longer than one week despite using milk of magnesia, stop taking it and see a doctor. Persistent constipation can signal an underlying condition that needs proper evaluation.
Chronic constipation is better managed with diet and lifestyle changes. Increasing fiber intake, drinking more water, and getting regular physical activity are the first-line strategies. These approaches address the root cause rather than just triggering a bowel movement.
How Does It Compare to Other Laxatives?
Milk of magnesia is one of several laxative types. Others include bulk-forming laxatives like psyllium, stimulant laxatives like bisacodyl, and stool softeners like docusate. They work differently and have different timing.
Bulk-forming laxatives, such as Metamucil, work by adding fiber to the stool. They are the gentlest option and are safe for daily use. They take 12 to 72 hours to work.
Stimulant laxatives work by triggering muscle contractions in the intestines. They act faster but are more likely to cause cramping. They are generally not recommended for long-term use.
Stool softeners work by allowing water and fats to mix into the stool. They are helpful when straining is the main problem, such as after surgery or childbirth.
Milk of magnesia sits between these in terms of speed and intensity. It is faster than bulk-forming laxatives but generally gentler than stimulant laxatives. For occasional constipation, it is a reasonable choice.
What About Drug Interactions?
Milk of magnesia can interfere with other medications. It can reduce the absorption of certain drugs, including some antibiotics, iron supplements, and thyroid medications. If you take prescription medications, space them at least two hours apart from milk of magnesia.
Specifically, magnesium can bind to tetracycline and fluoroquinolone antibiotics, making them less effective. It can also reduce absorption of digoxin, a heart medication. Taking these medications together can lead to reduced drug effectiveness.
If you take daily medications, ask your pharmacist about potential interactions with magnesium hydroxide. Your pharmacist can tell you the safest timing for your specific medication list.
Frequently Asked Questions
How fast does milk of magnesia work?
Liquid milk of magnesia usually produces a bowel movement within 30 minutes to six hours. The chewable tablets take longer, often 6 to 12 hours.
Can I take milk of magnesia every day?
No. You should not use it daily for more than one week without a doctor’s supervision. Regular use can lead to laxative dependence and weakened bowel function.
Is milk of magnesia safe during pregnancy?
Talk to your doctor before using it during pregnancy. It is generally considered low risk, but no medication should be assumed safe without medical guidance.
What happens if I take too much milk of magnesia?
Taking too much can cause severe diarrhea, cramping, and dangerous magnesium levels in the blood. Seek emergency care if you experience confusion, muscle weakness, or an irregular heartbeat.
