Milk of Magnesia and Maalox are not the same product. They share one ingredient, magnesium hydroxide, but differ in formulation, intended use, and how they work in your body. Milk of Magnesia is primarily a laxative that doubles as an antacid, while Maalox is a dedicated antacid with an added anti-gas ingredient.
How the Ingredients Differ
Milk of Magnesia contains a single active ingredient: magnesium hydroxide. It’s available in relatively high doses designed to draw water into the intestines, which softens stool and stimulates a bowel movement.
Maalox liquid contains three active ingredients per 5 mL teaspoon: 200 mg of aluminum hydroxide, 200 mg of magnesium hydroxide, and 20 mg of simethicone. The aluminum hydroxide and magnesium hydroxide work together to neutralize stomach acid, while simethicone breaks up gas bubbles to relieve bloating and pressure. The magnesium hydroxide dose in Maalox is much lower than what you’d take in a laxative dose of Milk of Magnesia.
Different Problems, Different Products
Milk of Magnesia is labeled for two uses. At lower doses, it can relieve heartburn, sour stomach, and acid indigestion. At higher doses, it treats occasional constipation, typically producing a bowel movement within 30 minutes to 6 hours. Most people reach for it specifically as a laxative.
Maalox targets a different set of symptoms: heartburn, acid indigestion, and gas. It is not designed to relieve constipation. The combination of aluminum hydroxide and magnesium hydroxide in Maalox is intentional. Magnesium tends to loosen stools, while aluminum tends to cause constipation. Pairing them helps balance out those opposing effects so your digestion stays more or less normal while you get acid relief.
Why You Can’t Swap One for the Other
If you’re constipated, Maalox won’t help. The magnesium hydroxide dose is too low to act as a laxative, and the aluminum hydroxide actually works against bowel motility. If you’re dealing with heartburn and gas, Milk of Magnesia will neutralize some acid but won’t address bloating the way simethicone does, and it may send you to the bathroom more than you’d like.
The products are also dosed differently. Milk of Magnesia’s antacid dose and laxative dose are not the same, and the label distinguishes between them. Maalox has a single dosing range because it serves one primary purpose: neutralizing acid and relieving gas.
Side Effects to Know About
Milk of Magnesia’s most common side effect is diarrhea, which is essentially its laxative action overshooting. Cramping can also occur. Maalox side effects are less common, but when they happen, they can go in either direction: diarrhea from the magnesium component or constipation from the aluminum component.
Both products carry a warning for people with kidney problems. Your kidneys are responsible for clearing excess magnesium from your blood. When kidney function drops significantly, magnesium from either product can build up to dangerous levels. This risk increases as kidney filtration falls below about 30 mL per minute and becomes especially concerning below 10 to 15 mL per minute. Aluminum can also accumulate in people with poor kidney function.
Drug Interactions Apply to Both
Because both products contain compounds that change your stomach’s acidity, they can interfere with how other medications are absorbed. Antacids containing magnesium hydroxide can bind to tetracycline and fluoroquinolone antibiotics, reducing their effectiveness. Certain heart and psychiatric medications may also be absorbed poorly when taken alongside antacids.
The interaction works the other way too. Some drugs, like certain decongestants, get absorbed more than expected when combined with antacids, raising the risk of side effects. If you take prescription medications regularly, spacing them at least two hours before or after either product is a good general practice.
Maalox Products Vary by Label
One source of confusion is that the Maalox brand name has appeared on several different formulations over the years. Some versions contain only aluminum hydroxide and magnesium hydroxide without simethicone. Others have been reformulated entirely. Always check the active ingredients on the specific bottle you’re buying rather than assuming all Maalox products are identical. The classic liquid antacid version includes all three ingredients: aluminum hydroxide, magnesium hydroxide, and simethicone.
Milk of Magnesia, by contrast, has stayed consistent. Whether you buy the Phillips’ brand or a store generic, the active ingredient is magnesium hydroxide. The main variation is concentration and flavor.
Choosing the Right One
Pick Milk of Magnesia if your main issue is constipation. It’s one of the most straightforward over-the-counter laxatives available, and it works by pulling water into the bowel rather than stimulating contractions, which tends to produce a gentler result. You can also use it at a lower dose for occasional heartburn, though it’s not the most convenient antacid option since the laxative effect may tag along.
Pick Maalox if your issue is heartburn, acid indigestion, or gas. The aluminum-magnesium combination provides acid neutralization with a more balanced effect on your bowels, and the simethicone addresses bloating that a plain antacid wouldn’t touch. It is not a substitute for a laxative.