Understanding Acid Reflux: What is known as an antacid?

October 14, 2025 •

4 min read

Over 60 million Americans experience heartburn at least once a month, often reaching for a common remedy to find relief [1.4.3]. So, what is known as an antacid? It is an over-the-counter medication that works by neutralizing stomach acid to soothe symptoms of heartburn and indigestion [1.2.1, 1.10.1].

Quick Summary

An antacid is a substance that neutralizes stomach acidity to relieve heartburn and indigestion. They work quickly by using alkaline compounds like calcium carbonate or magnesium hydroxide. This article explains how they function, the types, and risks.

Key Points

What it is: An antacid is a weak alkaline compound that neutralizes existing stomach acid to provide rapid relief from heartburn and indigestion [1.10.1].
How it works: Antacids work through a chemical reaction, raising the stomach's pH to make its contents less acidic and corrosive [1.2.5].
Common Ingredients: Key active ingredients include calcium carbonate, magnesium hydroxide, aluminum hydroxide, and sodium bicarbonate [1.3.1, 1.3.2].
Best Use: They are best for providing immediate, short-term relief for occasional symptoms, not for chronic conditions [1.7.1].
Side Effects: Common side effects include constipation (from aluminum/calcium) or diarrhea (from magnesium). Long-term use carries risks like electrolyte imbalance [1.5.5].
vs. Other Meds: Unlike H2 blockers and PPIs which reduce acid production, antacids only neutralize acid that is already present [1.7.1].
When to See a Doctor: If you need antacids more than twice a week or for longer than two weeks, consult a doctor as it may indicate a more serious issue [1.10.2, 1.11.2].

What is an Antacid and How Does It Work?

An antacid is an over-the-counter (OTC) medication designed to provide fast relief from the symptoms of excess stomach acid, such as heartburn, indigestion, and sour stomach [1.10.1]. The primary mechanism of action for an antacid is chemical neutralization [1.2.2]. The stomach naturally produces hydrochloric acid, a strong acid that helps digest food. When this acid flows back into the esophagus, it causes the burning sensation known as heartburn because the esophagus isn't protected like the stomach [1.10.1].

Antacids are weak bases (alkaline compounds) that directly counteract this acid [1.3.4]. When an antacid enters the stomach, it engages in a neutralization reaction with the hydrochloric acid, raising the stomach's pH level [1.2.5]. This process makes the stomach contents less corrosive, providing rapid symptom relief [1.9.3]. Beyond neutralization, some antacids can also inhibit the activity of pepsin, a digestive enzyme that can be damaging to the esophagus, and bind to bile acids [1.2.1, 1.2.5].

Common Types and Active Ingredients

Antacids are available in various forms, including chewable tablets, liquids, and powders, and their properties depend on their active ingredients [1.10.1].

Main Active Ingredients:

Calcium Carbonate: A potent and fast-acting ingredient, calcium carbonate is effective for quick relief [1.3.2, 1.9.3]. It reacts with stomach acid to form calcium chloride, water, and carbon dioxide. It is a common ingredient in products like Tums [1.3.2].
Magnesium Salts (Hydroxide, Carbonate): These are also fast-acting. Magnesium hydroxide reacts with stomach acid to create magnesium chloride and water [1.2.5]. However, magnesium-containing antacids are known to have a laxative effect and can cause diarrhea [1.3.2, 1.5.5].
Aluminum Hydroxide: This ingredient works more slowly than magnesium or calcium salts [1.3.2]. It is often combined with magnesium hydroxide to balance out gastrointestinal side effects, as aluminum can cause constipation [1.3.2, 1.3.5]. This combination is found in products like Mylanta [1.10.1].
Sodium Bicarbonate: Found in products like Alka-Seltzer, sodium bicarbonate is a rapidly acting antacid [1.3.2, 1.10.1]. It reacts with stomach acid to produce salt, water, and carbon dioxide gas, which can lead to belching [1.3.2]. Due to its high sodium content, it's not recommended for individuals on a low-sodium diet [1.3.2].
Alginic Acid: Often found in combination with other antacids (like in Gaviscon), alginic acid is an inactive ingredient that forms a foam barrier on top of the stomach contents. This 'raft' physically prevents acid from refluxing into the esophagus [1.3.4, 1.3.5].

Conditions Treated and Potential Side Effects

Antacids are primarily used for occasional, mild symptoms of heartburn and indigestion [1.5.5]. They are effective for providing immediate, short-term relief [1.7.1].

While generally safe when used as directed, antacids can have side effects, especially with long-term or excessive use [1.10.1].

Gastrointestinal Issues: The most common side effects are related to digestion. Magnesium-based antacids can cause diarrhea, while aluminum and calcium-based ones can cause constipation [1.5.5].
Acid Rebound: Overuse of some antacids, particularly calcium carbonate, can lead to a phenomenon called acid rebound, where the stomach produces even more acid after the medication wears off [1.5.2].
Electrolyte Imbalances: Chronic use can disrupt the body's mineral balance. For instance, aluminum-containing antacids can deplete phosphate and calcium, potentially leading to weakened bones (osteopenia) over time [1.5.1, 1.5.2]. Excessive intake of calcium carbonate can lead to high calcium levels in the blood (hypercalcemia) and, in rare cases, kidney stones [1.5.2, 1.5.5].
Drug Interactions: Antacids can interfere with the absorption of many other drugs by changing the stomach's pH or by binding directly to the other medication [1.6.3]. It is recommended to separate antacid administration from other drugs by at least 2 hours [1.3.3]. Significant interactions can occur with antibiotics (like tetracyclines and fluoroquinolones), iron supplements, and certain heart medications [1.6.1, 1.6.3].

Antacids vs. Other Acid Reducers

It's important to distinguish antacids from other classes of drugs that manage stomach acid, such as H2 blockers and Proton Pump Inhibitors (PPIs). While antacids neutralize existing acid, H2 blockers and PPIs work by reducing or stopping the production of stomach acid [1.7.1, 1.7.3].


Feature	Antacids (e.g., Tums, Mylanta)	H2 Blockers (e.g., Pepcid)	Proton Pump Inhibitors (PPIs) (e.g., Prilosec, Nexium)
Mechanism	Neutralizes existing stomach acid [1.7.3].	Blocks histamine signals that trigger acid production [1.7.1].	Blocks the enzyme that pumps acid into the stomach [1.7.1].
Onset of Relief	Within minutes [1.9.1].	About 30-45 minutes [1.9.1].	Takes 2-3 hours to take effect; may take 1-4 days for full effect [1.7.2, 1.9.1].
Duration of Relief	Short-acting (20-30 minutes) [1.9.1].	Lasts 4-12 hours [1.7.3, 1.9.1].	Longest-lasting relief (12-24 hours) [1.9.1].
Best Use	Occasional, infrequent heartburn for immediate relief [1.7.1].	Relief and prevention of mild to moderate heartburn [1.9.1].	Frequent heartburn (more than twice a week) and chronic conditions like GERD [1.7.1, 1.9.1].

Lifestyle Changes to Complement Treatment

For many, managing acid reflux involves more than just medication. Lifestyle adjustments can significantly reduce the frequency and severity of symptoms.

Dietary Modifications: Avoid common trigger foods such as spicy foods, fatty or fried foods, chocolate, citrus, tomatoes, caffeine, and alcohol [1.8.1, 1.8.2]. Eating smaller, more frequent meals can also help [1.8.2].
Maintain a Healthy Weight: Excess weight puts pressure on the abdomen, which can push acid into the esophagus. Losing even a small amount of weight can provide relief [1.8.2].
Adjust Habits: Avoid eating within 2-3 hours of bedtime and elevate the head of your bed by 6-8 inches [1.8.2]. Quitting smoking is also crucial, as smoking can weaken the muscle that keeps acid in the stomach [1.8.2].

Conclusion

What is known as an antacid is a go-to remedy for the discomfort of occasional heartburn, offering fast and effective relief by neutralizing stomach acid. With a variety of active ingredients like calcium carbonate and magnesium hydroxide, they address symptoms on the spot. However, they are not intended for chronic use, as this can lead to side effects and mask more serious underlying conditions [1.10.2]. If you find yourself needing an antacid more than twice a week, it's essential to consult a healthcare provider to explore the root cause and discuss longer-term treatment options like H2 blockers or PPIs, alongside beneficial lifestyle changes [1.10.2].

For more information, consult the U.S. Food and Drug Administration.

Frequently Asked Questions

Antacids are the fastest-acting heartburn remedy, typically providing relief in less than five minutes by neutralizing stomach acid on contact [1.9.1, 1.9.3].

Antacids are intended for occasional, short-term use. Taking them daily for long periods is not recommended without a doctor's advice, as it can lead to side effects and may mask an underlying condition that needs different treatment [1.10.1, 1.10.2].

An antacid neutralizes existing stomach acid for fast, temporary relief. A Proton Pump Inhibitor (PPI) works by blocking the production of stomach acid, providing longer-lasting relief and is intended for frequent or chronic heartburn [1.7.1, 1.7.3].

Yes. Antacids containing magnesium may cause diarrhea, while those with aluminum or calcium are more likely to cause constipation [1.5.5]. Combination products often balance these effects [1.3.2].

Yes, antacids can interfere with the absorption of many other drugs. You should take antacids at least two hours apart from other medications to avoid interactions [1.3.3]. They commonly interact with certain antibiotics, iron supplements, and heart medications [1.6.1].

Acid rebound is a side effect where the stomach overcompensates after the antacid wears off by producing an even larger amount of acid, which can worsen symptoms. This is sometimes associated with the overuse of certain antacids like calcium carbonate [1.5.2].

Alginate, or alginic acid, is an ingredient in some antacids (like Gaviscon) that creates a foam raft that floats on top of the stomach contents. This forms a physical barrier that helps prevent acid from splashing back into the esophagus [1.3.4, 1.3.5].