Mylanta is not a laxative. It is an antacid designed to neutralize stomach acid and relieve heartburn, indigestion, and gas. However, one of its active ingredients, magnesium hydroxide, is the same compound found in dedicated laxative products like Milk of Magnesia. At the doses used in Mylanta, this ingredient can loosen stools or cause diarrhea as a side effect, which is likely why many people wonder whether it doubles as a laxative.
What Mylanta Actually Contains
Mylanta Maximum Strength liquid contains three active ingredients per two-teaspoon dose: 800 mg of aluminum hydroxide, 800 mg of magnesium hydroxide, and 80 mg of simethicone. The aluminum hydroxide and magnesium hydroxide work together to neutralize stomach acid. Simethicone breaks up gas bubbles in the digestive tract, which helps with bloating and pressure.
The formula pairs aluminum and magnesium intentionally because their digestive side effects tend to cancel each other out. Aluminum hydroxide on its own tends to cause constipation, while magnesium hydroxide tends to cause loose stools. Together, they aim for a neutral effect on bowel habits, though in practice one side often wins out slightly.
Why Magnesium Hydroxide Has a Laxative Effect
Magnesium ions are poorly absorbed in the intestine. When they sit in the intestinal lumen, they pull water in through osmosis, increasing the fluid content of whatever is moving through your gut. This makes stool softer and easier to pass. At the same time, magnesium may trigger the release of certain gut hormones, including cholecystokinin, which speeds up intestinal movement.
This is exactly the mechanism that makes Milk of Magnesia work as a laxative. The difference is dosage. A typical laxative dose of magnesium hydroxide is 2,400 mg or more, while a single dose of Mylanta Maximum Strength delivers 800 mg. That’s enough to affect some people’s bowel habits, but it’s not formulated or dosed to treat constipation.
Diarrhea as a Side Effect
Diarrhea is actually more common than constipation with Mylanta, according to drug reference information from Kaiser Permanente. The magnesium content is the reason. This doesn’t mean Mylanta is acting “as a laxative” in a therapeutic sense. It means the magnesium component is having its natural osmotic effect on the gut, even at antacid-level doses.
If you’re taking Mylanta occasionally for heartburn and notice looser stools, this is a recognized side effect rather than a sign that something is wrong. But if diarrhea becomes persistent or bothersome, it’s worth switching to an antacid that doesn’t contain magnesium, such as one based purely on calcium carbonate.
Should You Use Mylanta for Constipation?
Using Mylanta to relieve constipation is not a good idea, even though it contains a laxative ingredient. The aluminum hydroxide works in the opposite direction, promoting constipation, so the net effect is unpredictable. You’d also be taking an acid-neutralizing product you don’t need, which can interfere with digestion and the absorption of other medications.
If you need an osmotic laxative, magnesium hydroxide is available in products specifically designed for that purpose, at appropriate doses and without the aluminum hydroxide that counteracts the effect. Those products also come with dosing instructions calibrated for constipation relief rather than acid neutralization.
Dosing Limits and Safety Considerations
The recommended adult dose of Mylanta Maximum Strength is 10 to 20 mL (one to two doses) taken between meals or at bedtime. The maximum is 60 mL (six doses) in any 24-hour period. Staying within these limits keeps magnesium intake at a level most healthy adults can handle without trouble.
People with kidney problems need to be particularly careful with any magnesium-containing product, including Mylanta. Healthy kidneys efficiently clear excess magnesium from the blood, but when kidney function is reduced, magnesium can accumulate to dangerous levels. This condition, called hypermagnesemia, can cause symptoms ranging from nausea and fatigue to dangerously low blood pressure and slowed heart rate. It’s most commonly seen in people with chronic kidney disease who take magnesium-containing antacids or laxatives regularly.