Can taking antacids cause diarrhea? Understanding ingredient-specific side effects

October 12, 2025 •

4 min read

According to MedlinePlus, brands of antacids containing magnesium are a known cause of diarrhea due to their laxative properties. This common side effect is specifically linked to the active ingredient, making the answer to the question, can taking antacids cause diarrhea?, dependent on the type of antacid you choose. Understanding which compounds affect bowel movements is crucial for managing digestive comfort.

Quick Summary

Antacids can cause diarrhea, primarily if they contain magnesium compounds that exert a laxative effect. Conversely, aluminum- or calcium-based antacids often cause constipation. Combination products balance these effects. Ingredient awareness is key for managing digestive side effects from these common over-the-counter medications.

Key Points

Magnesium is the Cause: Antacids containing magnesium, such as Milk of Magnesia, are the primary cause of diarrhea due to their laxative properties.
Check Active Ingredients: The specific side effect, whether diarrhea or constipation, is determined by the main mineral in the antacid formulation; always check the label.
Combination Products Offer Balance: Antacids that combine both magnesium and aluminum are designed to balance the laxative and constipating effects, minimizing significant changes in bowel habits.
Mechanism of Action: Magnesium causes diarrhea by creating an osmotic effect, drawing water into the intestinal lumen and resulting in looser, more frequent stools.
Chronic Use Risks: Excessive or chronic use of any antacid should be discussed with a doctor, as it can be linked to more serious issues, including an increased risk of infection.
Alternatives Exist: If magnesium-based antacids cause bothersome diarrhea, alternatives like calcium-based antacids, H2 blockers, or PPIs can be used to manage heartburn.

The Science Behind Antacid-Induced Diarrhea

Antacids are a common over-the-counter remedy for heartburn, indigestion, and acid reflux. They work by neutralizing excess stomach acid to provide quick, temporary relief. However, the active ingredients that produce this acid-neutralizing effect can also influence your digestive system in unintended ways. The most prominent cause of antacid-induced diarrhea is magnesium, which is often found in various liquid and chewable antacid formulations. Magnesium compounds, such as magnesium hydroxide, are known to have a laxative effect.

When magnesium enters the digestive system, it creates an osmotic gradient, meaning it pulls water from the surrounding tissues into the intestines. This increase in water content softens the stool and stimulates bowel movements, leading to diarrhea. Many antacid products contain a combination of ingredients to help counteract these opposing effects. For example, some formulations combine magnesium hydroxide with aluminum hydroxide. The aluminum in these products tends to cause constipation, which helps to balance the laxative effect of the magnesium. However, excessive use or a high ratio of magnesium to aluminum can still result in loose stools.

Magnesium-Based Antacids: The Primary Culprits

Antacids that rely heavily on magnesium as their active ingredient are the most likely to cause diarrhea. A well-known example is Milk of Magnesia, which is primarily magnesium hydroxide and is also sold as a saline laxative. Other products like Maalox and Mylanta also contain magnesium hydroxide. These formulations provide rapid relief for heartburn but can lead to frequent, watery bowel movements, particularly with high doses or continued use. For individuals with kidney problems, taking magnesium-based antacids can be particularly risky as impaired kidney function can lead to an accumulation of magnesium in the blood, a condition known as hypermagnesemia, which can cause serious complications.

Aluminum and Calcium-Based Antacids: The Constipation Counterparts

Conversely, antacids containing aluminum or calcium are more likely to cause constipation. Aluminum-based antacids, such as Amphojel, can slow down bowel movements. Calcium-based antacids, like Tums and Rolaids (which also contain magnesium), are also known to cause constipation. This is why many manufacturers create combination antacids, using a blend of magnesium and aluminum, to achieve a more neutral effect on the bowels. For individuals who experience diarrhea from a magnesium-containing antacid, switching to a calcium or aluminum-based product may provide relief, though it could introduce the opposite problem.

Managing and Preventing Antacid-Induced Diarrhea

If you find that your antacid is causing diarrhea, you have several options to manage the situation and find a more suitable solution for your heartburn. The first step is to check the active ingredients list on your medication and determine if it contains magnesium. If it does, consider switching to an alternative product that is magnesium-free. Many effective antacids use only calcium carbonate or a combination of aluminum and magnesium designed to prevent such side effects.

Lifestyle and dietary adjustments:

Avoid trigger foods: Foods that can exacerbate acid reflux and indigestion, like spicy foods, fatty meals, and caffeine, should be limited or avoided.
Eat smaller, more frequent meals: This reduces pressure on the stomach and the lower esophageal sphincter, minimizing the chance of acid reflux.
Stay hydrated: Drinking plenty of water can help flush out the excess minerals and support healthy digestion, especially if experiencing mild diarrhea.
Chew gum: Chewing sugar-free gum can stimulate saliva production, which helps to neutralize stomach acid and clear the esophagus.

Considering Alternatives for Persistent Heartburn

For those who experience persistent heartburn and find that antacids are causing undesirable side effects, speaking with a healthcare professional is recommended. Your doctor may suggest a different class of medication, such as H2 blockers or proton pump inhibitors (PPIs). H2 blockers, like Pepcid, decrease the amount of acid produced by the stomach. PPIs, such as Prilosec, are even more potent in reducing stomach acid. While these medications can also have side effects, including diarrhea in some cases, they offer an alternative for managing chronic acid reflux.

Comparison of Common Antacid Ingredients


Active Ingredient	Common Examples	Primary Side Effect	Mechanism
Magnesium Hydroxide	Milk of Magnesia, Maalox, Mylanta	Diarrhea	Draws water into the intestines (osmotic laxative)
Aluminum Hydroxide	Amphojel, Maalox, Mylanta	Constipation	Slows down bowel movements
Calcium Carbonate	Tums, Rolaids	Constipation	Can slow down bowel movements
Sodium Bicarbonate	Alka-Seltzer	Fluid retention, bloating	High sodium content can cause issues for those on restricted diets

Conclusion

In short, the answer to "can taking antacids cause diarrhea?" is a definitive yes, but it largely depends on the specific active ingredients in the product. Magnesium-based antacids are the main cause of this side effect due to their osmotic laxative properties. Aluminum and calcium-based antacids, on the other hand, are more likely to cause constipation. By understanding the composition of your medication, you can make an informed choice to minimize digestive discomfort. For individuals with persistent heartburn or those who experience severe or frequent diarrhea from their antacids, consulting a doctor is essential to explore alternative treatments, such as H2 blockers or PPIs, and rule out more serious underlying conditions. For additional information on antacid use and side effects, you can visit the MedlinePlus Medical Encyclopedia.

Frequently Asked Questions

Magnesium-containing antacids, like Milk of Magnesia or combination products that use magnesium hydroxide, are the most likely to cause diarrhea due to their laxative properties.

Magnesium draws water from the body into the intestinal lumen, a process known as an osmotic effect. This increases the water content of the stool, softening it and stimulating bowel movements, which can result in diarrhea.

While it is possible, the risk is lower than with pure magnesium antacids. The aluminum in the formulation often helps to counteract the laxative effect of the magnesium, leading to a more balanced effect on bowel function.

If the diarrhea is mild and temporary, you may not need to stop. However, if it persists, becomes severe, or is accompanied by other symptoms, you should consult your doctor. They may recommend switching to a different type of antacid or an alternative medication.

Alternatives for managing heartburn include switching to a calcium or aluminum-based antacid. For persistent issues, a doctor may recommend H2 blockers (like Pepcid) or proton pump inhibitors (PPIs).

Mild diarrhea is a common side effect of magnesium-based antacids and is not usually serious. However, persistent or severe diarrhea, especially with fever or blood, should be evaluated by a healthcare professional as it could indicate a more serious condition, like a C. difficile infection.

To manage mild diarrhea, consider switching to an antacid based on calcium or aluminum, as these tend to cause constipation. You can also reduce your dosage or use a combination product that has a more balanced effect on the gut.