Mylanta and Milk of Magnesia are not the same product. They share one ingredient, magnesium hydroxide, but Mylanta contains two additional active ingredients that give it a different purpose. Milk of Magnesia is a single-ingredient product used primarily as a laxative and simple antacid, while Mylanta is a combination antacid designed to neutralize stomach acid and relieve gas.
How the Ingredients Differ
Milk of Magnesia contains only magnesium hydroxide. Mylanta Maximum Strength contains three active ingredients per two-teaspoon dose: 800 mg of aluminum hydroxide, 800 mg of magnesium hydroxide, and 80 mg of simethicone. That overlap in magnesium hydroxide is likely why these two products get confused, but the additions in Mylanta change what the product does and how your body responds to it.
Aluminum hydroxide is a second antacid that works alongside magnesium hydroxide to neutralize stomach acid more effectively. It also has a constipating effect, which partially offsets the loosening effect magnesium hydroxide has on your bowels. Simethicone is a gas-relief agent. It works as a surfactant, lowering the surface tension of gas bubbles in your digestive tract so they merge together and pass more easily as belching or flatulence. It doesn’t reduce how much gas your body produces; it just helps the gas move out instead of sitting in your gut causing bloating and discomfort.
What Each Product Is Designed to Treat
Milk of Magnesia is most commonly used as an osmotic laxative. It draws water into your intestines, softening stool and triggering a bowel movement, typically by the next morning. At lower doses, magnesium hydroxide also works as a mild antacid for occasional heartburn or indigestion, but laxative use is its primary role on drugstore shelves.
Mylanta targets a different set of symptoms: heartburn, acid indigestion, sour stomach, and the bloating or pressure that comes with trapped gas. The combination of two antacids neutralizes acid quickly, while the simethicone component addresses gas. If constipation relief is what you need, Mylanta is not a substitute for Milk of Magnesia. And if gas and acid reflux are your main complaints, Milk of Magnesia won’t address the gas at all.
How Dosing Changes the Effect
An interesting detail about magnesium hydroxide is that its effect depends heavily on dose. In Japan, where dosing guidelines draw a clear line, 500 to 1,000 mg per day is considered an antacid dose, while 2,000 mg per day is the laxative dose. This explains why Mylanta, which contains magnesium hydroxide at antacid-level amounts alongside aluminum hydroxide, doesn’t typically cause the same bowel-loosening effect as a full dose of Milk of Magnesia. The aluminum hydroxide in Mylanta also has a binding, constipating quality that counterbalances the magnesium.
Milk of Magnesia, taken at its full recommended laxative dose, delivers a higher concentration of magnesium hydroxide with nothing to slow down the bowel stimulation. That’s why it reliably produces a bowel movement within 6 to 8 hours for most people.
Kidney Health and Magnesium Buildup
Both products carry a shared risk because they both contain magnesium hydroxide. Your kidneys are responsible for clearing excess magnesium from your body. When kidney function is significantly reduced, particularly when filtration drops below 30 mL per minute, the kidneys can no longer keep up. Magnesium accumulates in the blood, a condition called hypermagnesemia, which can cause muscle weakness, low blood pressure, and in severe cases, cardiac problems.
This risk applies to both Mylanta and Milk of Magnesia, but it’s especially relevant with Milk of Magnesia because the laxative dose delivers more magnesium per serving. If you have chronic kidney disease or have been told your kidney function is impaired, neither product should be used casually.
Use During Pregnancy
Milk of Magnesia is generally considered safe for pregnancy constipation. The Mayo Clinic lists magnesium hydroxide among laxatives that pregnant women can use. Because constipation is one of the most common pregnancy complaints, Milk of Magnesia is a frequent recommendation.
Mylanta is sometimes used during pregnancy for heartburn, which is also extremely common, particularly in the second and third trimesters. The aluminum hydroxide component is the main consideration here, as aluminum-containing antacids are typically used only for short-term relief during pregnancy rather than daily use.
Choosing Between Them
The choice comes down to your symptoms. If you’re dealing with constipation and need help moving things along, Milk of Magnesia is the appropriate product. If your problem is heartburn, acid stomach, or uncomfortable bloating from gas, Mylanta addresses all three of those symptoms in a single dose. Using one in place of the other won’t give you the relief you’re looking for, despite the shared ingredient.
Both are available over the counter and intended for short-term, occasional use. If you find yourself reaching for either product regularly, that pattern is worth paying attention to, as frequent heartburn, chronic constipation, and persistent bloating can all signal underlying conditions that benefit from a different approach than antacids or laxatives alone.