Maalox is not a laxative. It is an over-the-counter 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 Milk of Magnesia, a well-known laxative. This overlap is why the question comes up so often, and why some people do notice changes in their bowel habits when taking Maalox.
What Maalox Actually Contains
Each 5 mL (one teaspoon) dose of Maalox liquid contains 200 mg of aluminum hydroxide, 200 mg of magnesium hydroxide, and 20 mg of simethicone. The first two ingredients neutralize acid in the stomach. Simethicone helps break up gas bubbles. None of these ingredients are included at doses intended to produce a laxative effect.
The key detail is how those two antacid ingredients interact with digestion. Magnesium hydroxide draws water into the intestines, which can loosen stools. Aluminum hydroxide does the opposite: it tends to cause constipation. Antacid manufacturers combine the two specifically so their bowel effects cancel each other out. In theory, you get acid relief without significant changes in how your gut moves.
Why Magnesium Hydroxide Has a Laxative Reputation
Magnesium hydroxide works as a laxative through a straightforward process. Magnesium ions are poorly absorbed in the intestines. When they sit in the intestinal lumen, they create osmotic pressure that pulls water in from surrounding tissue. This extra fluid softens stool and increases its volume, which stimulates the intestines to contract and move things along.
The difference between an antacid effect and a laxative effect comes down to dose. A standard Maalox dose delivers 200 mg of magnesium hydroxide. A standard laxative dose of concentrated Milk of Magnesia delivers 3,600 to 7,200 mg of magnesium hydroxide, roughly 18 to 36 times more. At 200 mg, there simply isn’t enough magnesium hydroxide reaching the lower intestines to produce a reliable laxative effect in most people.
Can Maalox Still Affect Your Bowels?
Yes, though it’s uncommon. Clinical data shows that both diarrhea and constipation occur in roughly 0.1% to 1% of people taking Maalox at recommended doses. Some people are more sensitive to magnesium’s water-drawing effect, and if you take Maalox frequently or at higher-than-recommended amounts, the magnesium can accumulate enough to loosen stools noticeably.
If you’re taking Maalox and experiencing loose stools, the magnesium component is the likely cause. On the flip side, if you notice constipation, the aluminum hydroxide is probably the dominant effect for your body. Neither side effect is dangerous at normal doses for most people, but persistent digestive changes are worth paying attention to.
Who Should Be Careful
People with kidney problems face a specific risk with magnesium-containing antacids like Maalox. Healthy kidneys efficiently clear excess magnesium from the blood, but compromised kidneys cannot keep up. This can lead to a dangerous buildup of magnesium in the bloodstream, a condition called hypermagnesemia. Case reports have documented fatal outcomes in patients with impaired kidney function who regularly used magnesium hydroxide products. If your kidneys don’t function normally, magnesium-containing antacids require medical guidance.
For people with healthy kidneys, the magnesium in a standard Maalox dose poses no meaningful risk. Your body simply excretes what it doesn’t need.
If You Actually Need a Laxative
Using Maalox as a laxative would be ineffective and misguided. You’d need to take many times the recommended antacid dose to approach a laxative-level amount of magnesium hydroxide, and in doing so you’d also consume large amounts of aluminum hydroxide, which works against the laxative effect and can cause constipation on its own.
If you’re looking for an osmotic laxative, Milk of Magnesia is the appropriate product. It contains magnesium hydroxide at concentrations specifically formulated for that purpose, without the constipating aluminum counterpart. A typical adult laxative dose generally produces a bowel movement within 30 minutes to 6 hours, depending on the individual and whether the stomach is empty or full.