Which antacid is most likely to cause constipation?

October 12, 2025 •

3 min read

Over-the-counter antacids are a popular and fast-acting solution for heartburn, but millions of users have experienced an unwanted side effect: constipation. Certain types of antacids, most notably those containing aluminum or calcium, are recognized as the primary culprits. Understanding which antacid is most likely to cause constipation can help you make a better choice for your digestive health.

Quick Summary

Aluminum and calcium-based antacids are the primary culprits for inducing constipation by slowing intestinal motility and forming insoluble compounds. Magnesium-containing antacids, conversely, often cause diarrhea, leading many combination formulas to balance these opposing effects.

Key Points

Aluminum-Based Antacids: Ingredients like aluminum hydroxide are most likely to cause constipation by slowing intestinal muscles.
Calcium-Based Antacids: Products containing calcium carbonate, such as Tums, are also major causes of constipation.
Magnesium-Based Antacids: Ingredients like magnesium hydroxide typically cause diarrhea, and are often combined with aluminum to balance side effects.
Combination Antacids: Products that mix aluminum and magnesium are less likely to cause significant changes in bowel habits.
Constipation Mechanism: Aluminum and calcium can slow intestinal motility and form insoluble salts, leading to slower digestion and harder stools.
Management Strategies: Increasing fluids and fiber, exercising, and considering a different antacid type can help prevent and relieve antacid-induced constipation.

The Primary Culprits: Aluminum and Calcium

When seeking relief from heartburn or indigestion, it is important to know which antacids carry a higher risk of causing constipation. The most likely to cause constipation are those containing either aluminum hydroxide or calcium carbonate. These ingredients can significantly disrupt normal bowel function, especially with regular or high-dose use.

Aluminum's Mechanism: Slowing Down Gut Motility

Aluminum-based antacids, such as aluminum hydroxide, are known to have an inhibitory effect on intestinal smooth muscles, which slows down the movement of waste through the digestive tract. Furthermore, aluminum can bind with phosphate in the gut to form insoluble aluminum phosphate complexes. This process decreases the intestinal fluid content and reduces the propulsive contractions necessary for regular bowel movements, leading to delayed transit and constipation. Chronic use can, in rare but severe cases, lead to bowel obstruction.

Calcium's Mechanism: Reduced Intestinal Fluid

Calcium carbonate, the active ingredient in popular antacid brands like Tums and Rolaids, is also a well-documented cause of constipation. Like aluminum, excessive calcium can slow down intestinal motility. It may also decrease fluid secretion in the intestines, which results in harder, drier stools that are more difficult to pass. The combination of slowed movement and reduced fluid contributes to the constipating effect, a side effect many supplement users also report.

Combination and Magnesium Antacids: The Balancing Act

To counter the constipating effects of aluminum and calcium, many manufacturers produce combination antacids. These products often pair aluminum hydroxide with magnesium hydroxide. Magnesium has the opposite effect on the bowels, acting as an osmotic laxative by drawing water into the intestines, which promotes bowel movements and can cause diarrhea. By combining these two active ingredients, manufacturers create a more neutral-acting formula that minimizes the risk of either constipation or diarrhea.

For those prone to constipation, magnesium-only antacids, such as Phillips' Milk of Magnesia, can be an effective way to relieve acid reflux symptoms without worsening bowel regularity. However, these can lead to diarrhea if not dosed carefully.

Comparison of Common Antacid Types


Antacid Type	Active Ingredient	Common Examples	Primary Digestive Side Effect
Aluminum-Based	Aluminum Hydroxide	Amphojel	Constipation
Calcium-Based	Calcium Carbonate	Tums, Rolaids	Constipation
Magnesium-Based	Magnesium Hydroxide	Phillips' Milk of Magnesia	Diarrhea
Combination	Aluminum + Magnesium	Maalox, Mylanta	Neutral (often balanced)
Sodium Bicarbonate	Sodium Bicarbonate	Alka-Seltzer	Belching, high sodium content

Managing and Preventing Antacid-Induced Constipation

If you find that an antacid is causing constipation, several strategies can help manage or prevent the side effect. Always consult a healthcare provider before making significant changes to your medication regimen, especially for chronic conditions.

Increase Fluid Intake: Drinking plenty of water is crucial. Dehydration is a major cause of constipation, and adequate hydration helps soften stools.
Boost Dietary Fiber: Adding high-fiber foods like fruits, vegetables, whole grains, and legumes can help promote regular bowel movements. Fiber supplements like psyllium (Metamucil) or methylcellulose (Citrucel) can also be effective.
Stay Active: Regular physical activity, even a daily walk, can help stimulate the digestive system and encourage regularity.
Consider Combination Formulas: Switching from a single-ingredient aluminum or calcium antacid to a combination product may help balance the side effects.
Explore Alternatives: For persistent heartburn, other options exist. Histamine-2 blockers (like famotidine) or proton pump inhibitors (PPIs) may be more appropriate for long-term use and can be discussed with your doctor.

Conclusion

In conclusion, when considering which antacid is most likely to cause constipation, the answer clearly points to those containing aluminum hydroxide and calcium carbonate. Their shared mechanism of slowing intestinal motility and forming compounds that interfere with bowel transit is the reason for this common side effect. For those susceptible to constipation, combination products with magnesium offer a more balanced option, and lifestyle adjustments like increasing fiber, fluids, and exercise can provide relief. Persistent or severe symptoms warrant a consultation with a healthcare professional, as an alternative treatment may be necessary. For more information on medications and their side effects, consider visiting Johns Hopkins Medicine.

Frequently Asked Questions

Antacids containing aluminum or calcium cause constipation by two main mechanisms. First, they can slow down the muscle contractions of the intestines (intestinal motility). Second, they can form insoluble compounds in the gut, which reduces the water content of the stool and makes it harder to pass.

Yes, Tums are likely to cause constipation. The active ingredient in Tums is calcium carbonate, which is well-known for its constipating effect, especially with frequent or high-dose use.

No, not all antacids cause constipation. Antacids containing magnesium, such as Milk of Magnesia, have a laxative effect and are more likely to cause diarrhea. Combination antacids that mix aluminum and magnesium are designed to minimize both constipation and diarrhea.

For someone prone to constipation, a good option is a combination antacid that includes magnesium hydroxide, such as Maalox or Mylanta. The magnesium helps counteract the constipating effects of the aluminum. Alternatively, magnesium-only antacids are an option but may cause diarrhea.

Yes, dietary changes can help. Increasing your intake of dietary fiber from fruits, vegetables, and whole grains can promote regular bowel movements. Staying well-hydrated is also essential, as sufficient fluid intake helps soften stool.

Yes, other medications treat heartburn with a lower risk of constipation. Histamine-2 (H2) blockers (like famotidine) and proton pump inhibitors (PPIs) (like omeprazole) reduce acid production rather than neutralizing it. However, it is best to discuss these options with a doctor.

You should see a doctor if your constipation is severe, persistent, or accompanied by other symptoms like abdominal pain. This is especially important for individuals with underlying health conditions, such as kidney disease, as excessive mineral intake can be harmful.