Is Gaviscon better than Rennie? A Comprehensive Comparison for Heartburn

October 6, 2025 •

3 min read

Nearly one in five people experience heartburn symptoms at least once a week. To determine if Is Gaviscon better than Rennie?, understanding their fundamental differences in relieving indigestion and acid reflux is key to choosing the right over-the-counter solution.

Quick Summary

This guide compares Gaviscon and Rennie, detailing their distinct mechanisms of action, ingredients, and ideal uses to help you select the most effective medication for your specific heartburn or acid reflux symptoms.

Key Points

Symptom-Dependent Choice: The best option depends on your specific symptoms—Rennie for rapid neutralization of simple heartburn, Gaviscon for acid reflux with regurgitation.
Mechanism of Action: Rennie is a basic antacid that neutralizes stomach acid, while Gaviscon creates a physical barrier (raft) in addition to neutralizing acid.
Alginate Raft: Gaviscon's key feature is the alginate raft, which is highly effective at preventing stomach acid from rising into the esophagus after a meal.
Speed vs. Duration: Rennie typically offers very fast relief, whereas Gaviscon provides more sustained protection, particularly for symptoms linked to acid reflux.
Ingredient Awareness: Check ingredients for sodium and calcium content, especially if you have high blood pressure or are prone to constipation, as this can influence your choice.
Consult a Pharmacist: If your symptoms are frequent or severe, or if you take other medications, it is wise to speak with a healthcare professional to ensure the correct choice.

Understanding the Mechanisms: Antacid vs. Alginate

At the core of the debate over whether Gaviscon is better than Rennie lies their different approaches to tackling indigestion and acid reflux. While both provide relief, their primary methods of action are distinct, which makes one potentially more effective than the other for certain symptoms.

How Rennie Works

Rennie functions primarily as a traditional antacid, using active ingredients like calcium carbonate and magnesium carbonate to neutralize excess stomach acid. This rapid neutralization increases the stomach's pH, reducing the burning sensation of heartburn and indigestion. Rennie's effects are typically fast-acting but may be shorter in duration compared to treatments addressing ongoing reflux.

How Gaviscon Works

Gaviscon, particularly formulations like Gaviscon Double Action, employs a dual mechanism. It contains antacids for neutralization and an alginate derived from seaweed. The alginate forms a protective raft that floats on stomach contents, creating a physical barrier to prevent acid from rising into the esophagus. This makes Gaviscon effective for post-meal reflux and symptoms like regurgitation. Studies show it is more effective than simple antacids at controlling postprandial esophageal acid exposure.

Comparison of Gaviscon and Rennie

Choosing between Gaviscon and Rennie depends on several factors, including active ingredients, mechanism, speed, duration, and suitability for different symptoms. The table below outlines their key differences.


Feature	Gaviscon	Rennie
Primary Mechanism	Dual-action: Antacid neutralizes, Alginate forms raft	Single-action: Antacid neutralizes
Active Ingredients	Sodium alginate, Sodium bicarbonate, Calcium carbonate	Calcium carbonate, Magnesium carbonate
Speed of Action	Quick neutralization and barrier formation	Very rapid neutralization
Duration of Effect	Sustained protection from barrier	Effective while active, potentially shorter duration
Best For	Heartburn with reflux/regurgitation, post-meal	Quick relief of mild heartburn/indigestion
Common Formulations	Liquids, Chewable Tablets	Chewable Tablets, Liquid

Choosing the Right Relief for Your Symptoms

The best choice is determined by the specific nature of your symptoms. Neither medication is universally superior.

When to Choose Gaviscon

Acid Reflux and Regurgitation: Choose Gaviscon if you experience acid or food coming back up, as the alginate raft blocks this.
Post-Meal Heartburn: It targets the post-meal 'acid pocket,' preventing reflux.
Need for Sustained Relief: Provides longer-lasting effects beneficial for symptoms persisting after eating.

When to Choose Rennie

Fast, Occasional Heartburn: Excellent for general, occasional heartburn needing rapid relief.
Milder Symptoms: Sufficient and effective for milder symptoms without significant regurgitation.
Simpler Ingredients: Preferred by some who are sensitive to alginates or the higher sodium in some Gaviscon products.

Important Considerations and Potential Side Effects

Consider potential side effects and health factors.

Sodium Content: Some Gaviscon formulations are high in sodium, a factor for those with hypertension or on a low-sodium diet.
Mineral Content: Rennie's calcium can cause constipation, while magnesium may cause diarrhea.
Drug Interactions: Both can affect other medications' absorption. Consult a pharmacist or doctor if taking other drugs.

Conclusion

Determining is Gaviscon better than Rennie? depends on your specific indigestion symptoms. Rennie offers rapid neutralization for simple heartburn. Gaviscon, with its alginate raft, provides targeted, sustained protection against acid reflux and regurgitation, particularly after meals. Understanding these differences helps in selecting the most effective treatment.

For more information on antacids, including their function and ingredient types, refer to the NHS overview.

Frequently Asked Questions

Combining Gaviscon and Rennie is generally not recommended unless advised by a healthcare professional. Both are intended to manage stomach acid, and using them together may lead to excessive neutralization or other adverse effects.

Rennie's antacid action generally works slightly faster for immediate acid neutralization, but Gaviscon's dual action also starts quickly, and its alginate raft provides a more targeted and sustained effect against reflux.

Gaviscon is generally considered better for acid reflux and regurgitation, especially after meals, because its alginate raft provides a physical barrier preventing acid from rising. Rennie is more suited for simple heartburn.

Yes. Gaviscon comes in formulations like Original, Advance, and Double Action, with varying strengths of alginate and antacids. Rennie primarily comes in chewable tablets but may also have liquid options, and some contain alginate.

Yes, common side effects can include constipation (from high calcium content in Rennie), diarrhea (from magnesium), and bloating. Some Gaviscon products are high in sodium, which should be considered by individuals with high blood pressure.

Antacids can interfere with the absorption of other medications. It is best to take them at a separate time from other oral medications or to consult a healthcare provider to ensure there are no interactions.

Liquid forms of Gaviscon often provide more coverage and form a more robust raft for reflux prevention. Chewable tablets for both products are convenient for on-the-go use, but the choice often comes down to personal preference for texture and taste.