Magnesium hydroxide is the most effective form of magnesium for acid reflux. It works as a direct antacid, neutralizing stomach acid on contact and providing noticeable heartburn relief in under 20 minutes. You’ll find it in familiar over-the-counter products like Milk of Magnesia and Maalox. Other magnesium salts, including magnesium carbonate and magnesium trisilicate, also neutralize acid but differ in speed and side effects. Forms like magnesium glycinate or magnesium citrate, popular as supplements, are not true antacids and won’t give you the same quick relief.
How Magnesium Hydroxide Neutralizes Acid
Your stomach produces hydrochloric acid with a pH that can drop to around 1.7 on an empty stomach. Magnesium hydroxide is an alkaline compound that reacts rapidly with this acid, converting it into magnesium chloride and water. That reaction raises your stomach’s pH toward a more neutral level, which directly reduces the burning sensation of acid reflux.
In clinical testing, a magnesium hydroxide-based antacid (Maalox) delivered meaningful heartburn relief within about 19 minutes, compared to 70 minutes for a common acid-reducing medication (ranitidine). The trade-off is duration: the neutralizing effect fades after roughly three hours, while medications that reduce acid production last longer. For occasional or mild reflux, that quick but shorter window is often exactly what people need.
Other Magnesium Salts That Work as Antacids
Magnesium hydroxide isn’t the only magnesium compound that neutralizes stomach acid. Two others show up in antacid formulations:
- Magnesium carbonate also reacts with stomach acid, but produces carbon dioxide gas as a byproduct. This can cause bloating or belching, which some people find uncomfortable, especially if reflux is already making them feel full or gassy.
- Magnesium trisilicate dissolves slowly and reacts more gradually with stomach acid. It produces silicon dioxide (silica) as a byproduct. Because it works slower, it’s less useful for fast relief but may offer a slightly longer buffering effect.
All three are classified as non-absorbable antacids, meaning they primarily act locally in the stomach rather than entering your bloodstream in large amounts. Their acid-neutralizing capacity is comparable when measured at equal volumes.
Why Magnesium Supplements Aren’t the Same
If you’ve seen magnesium glycinate, magnesium citrate, or magnesium oxide recommended online for reflux, it’s worth understanding why these don’t function the same way. These forms are designed to be absorbed into your bloodstream to raise your overall magnesium levels. They don’t sit in the stomach and neutralize acid the way magnesium hydroxide does.
There is some early evidence suggesting magnesium may play a broader role in reflux. Magnesium deficiency has been loosely linked to problems with esophageal motility and reflux, and one proposed mechanism is that adequate magnesium levels could help the stomach empty more efficiently, reducing the pressure that pushes acid upward. A small randomized study found magnesium supplementation improved symptoms of laryngopharyngeal reflux (a type of reflux that reaches the throat). But this research is preliminary, and taking a magnesium supplement is not a substitute for an antacid when you’re experiencing active heartburn.
Magnesium citrate deserves a specific caution. It’s a weak base, and there are anecdotal reports of esophageal irritation from swallowing undiluted magnesium citrate powder. If you take magnesium citrate as a supplement, always dissolve it fully in water and don’t take it dry.
The Laxative Effect and How to Manage It
The most common side effect of magnesium-based antacids is loose stools or diarrhea. Magnesium draws water into the intestines through osmosis, which is exactly why magnesium hydroxide doubles as a laxative at higher doses.
Research has established that supplemental magnesium above 350 mg per day frequently triggers cramping and diarrhea in adults. At much higher doses used in clinical studies (800 to 1,200 mg), diarrhea becomes significantly more common. For context, a standard dose of Milk of Magnesia as an antacid contains less magnesium than the laxative dose of the same product, so sticking to the antacid dosing on the label typically avoids this problem. If you find magnesium hydroxide loosens your stools even at antacid doses, products that combine it with aluminum hydroxide (like Maalox) help counterbalance this effect, since aluminum tends to be constipating.
Who Should Be Cautious
Healthy kidneys clear excess magnesium efficiently. But if your kidney function is reduced, magnesium can accumulate in your blood to potentially dangerous levels. The kidneys can generally compensate until filtration drops below about 30 mL/min. Below that threshold, and especially below 10 mL/min, the body loses its ability to regulate magnesium, and even standard antacid doses could cause a buildup. If you have chronic kidney disease, magnesium-based antacids are not a safe default choice.
Timing also matters if you take other medications. Magnesium antacids can interfere with the absorption of iron supplements, aspirin, and certain prescription drugs. The general rule is to separate your antacid from other medications by at least two hours.
Choosing the Right Product
For straightforward, occasional acid reflux, magnesium hydroxide in liquid form gives you the fastest relief. Liquid antacids coat the stomach lining more evenly than chewable tablets, which can improve how quickly they work. Look for it sold as Milk of Magnesia or in combination antacids that pair magnesium hydroxide with aluminum hydroxide.
If bloating is already part of your reflux symptoms, avoid magnesium carbonate, since the carbon dioxide it produces can make that worse. If you prefer a slower, gentler option and your symptoms are mild, magnesium trisilicate is an alternative, though it’s less commonly available as a standalone product.
For reflux that happens more than twice a week or persists for weeks, antacids of any kind are a temporary fix. They neutralize acid that’s already been produced but don’t address the underlying cause, whether that’s a weak lower esophageal sphincter, delayed stomach emptying, or another issue. Frequent reflux typically calls for a different class of treatment that reduces acid production rather than neutralizing it after the fact.