Milk of magnesia works well as a short-term remedy for acid reflux. It neutralizes stomach acid quickly and can relieve heartburn within minutes. But it’s designed for occasional use, not as a daily solution for chronic reflux, and it comes with some trade-offs worth understanding before you reach for the bottle.
How It Neutralizes Stomach Acid
The active ingredient in milk of magnesia is magnesium hydroxide. When it reaches your stomach, it reacts with hydrochloric acid to form magnesium chloride and water. This reaction is straightforward: it directly neutralizes the acid causing your discomfort. Unlike some antacids that generate carbon dioxide during this process (leading to bloating and burping), magnesium hydroxide doesn’t produce any gas.
It has a high neutralizing capacity, meaning a relatively small dose can handle a significant amount of acid. The relief tends to kick in fast, which is why magnesium-based antacids are among the most popular over-the-counter options for heartburn.
Dosing for Heartburn Relief
When used as an antacid (not a laxative), the typical adult dose is 1 to 3 teaspoons of the liquid suspension. You can take it with water, and you should shake the bottle well before measuring your dose. The antacid dose is considerably smaller than the laxative dose, which matters because taking too much increases your chances of side effects.
Don’t exceed the maximum recommended daily dose listed on the label, and avoid using it for more than two weeks without talking to a doctor. If your acid reflux is frequent enough that you’re reaching for milk of magnesia daily, that’s a sign something else may be going on.
Side Effects to Expect
The most common side effect is diarrhea. Magnesium draws water into the intestines, which is exactly why it works as a laxative at higher doses. Even at antacid doses, some people notice looser stools. You may also experience a decreased sense of taste, though this is less common and typically temporary.
This laxative tendency is actually one of the key differences between milk of magnesia and calcium-based antacids like Tums. Calcium carbonate tends to cause constipation, while magnesium hydroxide leans the other direction. Some people alternate between the two or use combination products to balance things out.
How It Compares to Other Antacids
Both magnesium-based and calcium-based antacids are fast-acting, but they have different side effect profiles. Calcium-based options like Tums and Rolaids are convenient (they come as chewable tablets) and provide supplemental calcium, but overuse can raise blood calcium levels and cause constipation. Milk of magnesia has stronger neutralizing power per dose but is more likely to cause diarrhea.
Neither type is ideal for managing chronic acid reflux on its own. Antacids treat symptoms after they appear. They don’t reduce the amount of acid your stomach produces or address the underlying cause of reflux, such as a weakened valve between the esophagus and stomach. For frequent reflux (two or more times a week), acid-reducing medications that work differently, like H2 blockers or proton pump inhibitors, are generally more effective long-term strategies.
Medications It Can Interfere With
Magnesium hydroxide can reduce your body’s ability to absorb several common medications. The ones most affected include:
- Certain antibiotics, including ciprofloxacin and tetracycline
- Thyroid medications like levothyroxine
- Iron supplements
- Digoxin, a heart medication
If you take any of these, separate them from your milk of magnesia dose by at least two hours. Taking them at the same time can mean your other medication doesn’t work as well as it should.
Risks of Using It Too Often
The biggest concern with prolonged use is a buildup of magnesium in the blood, a condition called hypermagnesemia. Your kidneys normally clear excess magnesium without trouble, but long-term daily use of magnesium-containing antacids can overwhelm that process, especially if your kidney function is even mildly reduced.
Early symptoms of excess magnesium include dizziness, nausea, and weakness. More severe cases can cause confusion, difficulty breathing, abnormal heart rhythms, and in rare extreme situations, cardiac arrest. People with any degree of kidney disease are at the highest risk, and dose adjustments may be necessary, though no specific guidelines exist for how much to reduce.
This is why milk of magnesia works best as an occasional tool rather than a daily habit. If you’re relying on it multiple times a week, that pattern itself is useful information: it suggests your reflux is frequent enough to benefit from a different treatment approach that addresses acid production rather than neutralizing it after the fact.