Gaviscon works by forming a physical barrier on top of your stomach contents, preventing acid from splashing up into your esophagus. Unlike most heartburn medications that reduce acid production, Gaviscon creates a floating gel “raft” that sits at the top of your stomach and acts as a lid. Relief typically begins within about 3 to 4 minutes of taking a dose.
The Raft That Floats on Your Stomach
The key ingredient in Gaviscon is sodium alginate, a compound derived from seaweed. When it hits the acid in your stomach, it transforms from a liquid into a gel. At the same time, bicarbonate in the formula reacts with stomach acid to produce tiny bubbles of carbon dioxide. These bubbles get trapped inside the gel, making it buoyant enough to float on top of whatever is in your stomach.
This floating gel is called a “raft,” and it does two things. First, it physically blocks stomach contents from rising into your esophagus. Second, if reflux does occur, the raft itself gets pushed up first, shielding your esophagus from direct contact with acid. This is especially effective when you’re upright, since the raft naturally positions itself right at the junction between your stomach and esophagus.
The raft also traps more than just acid. It captures pepsin (a digestive enzyme) and bile salts, both of which can damage the lining of your esophagus even in the absence of strong acid. The raft has enough capacity to absorb these irritants across multiple reflux episodes, not just one.
What’s Actually in Each Dose
Gaviscon comes in several formulations, and the ingredients vary depending on where you live and which version you buy. In the UK, Gaviscon Double Action contains 1,000 mg of sodium alginate, 426 mg of sodium bicarbonate, and 650 mg of calcium carbonate per 20 ml dose. The calcium carbonate also neutralizes some acid directly, giving it a dual role: part raft-builder, part traditional antacid.
US formulations use a different combination, typically aluminum hydroxide and magnesium carbonate as the antacid components. Each tablespoon of the regular-strength US liquid contains about 52 mg of sodium and 115 mg of magnesium. The extra-strength version contains less per dose (11 mg sodium, 75 mg magnesium per teaspoon) because the serving size is smaller.
How Fast It Works Compared to Other Treatments
Gaviscon is one of the fastest-acting heartburn treatments available. In a clinical study measuring time to relief after a single dose, heartburn was relieved in an average of 3.3 minutes. That speed comes from its mechanical action: it doesn’t need to be absorbed into your bloodstream or shut down acid-producing cells. It simply forms a barrier on contact with stomach acid.
Proton pump inhibitors (PPIs) like omeprazole work very differently. They block the cellular machinery that produces acid in the first place, but this takes time. Omeprazole shuts down about 70% of acid production on the first day, with full effectiveness building over two to three days. In a head-to-head trial, both Gaviscon and omeprazole took an average of 2.0 days to produce the first full 24-hour heartburn-free period, and roughly 90% of patients in both groups achieved that milestone. By day 7, omeprazole pulled slightly ahead, producing an average of 3.7 heartburn-free days versus 3.1 for Gaviscon. But there was no significant difference in pain intensity reduction at either the one-week or two-week mark.
The practical takeaway: Gaviscon works faster in the moment, while PPIs build a more sustained suppression of acid over days. Many people use Gaviscon for occasional flare-ups and PPIs for chronic reflux, though the two can also be used together.
Safety During Pregnancy and Breastfeeding
Gaviscon is considered safe during pregnancy, which matters because heartburn affects a large proportion of pregnant women, particularly in the third trimester. The NHS confirms it can be taken during pregnancy as long as you follow the recommended dosage. It can also be taken while breastfeeding, as it is not expected to cause any effects in the baby. Because Gaviscon works locally in the stomach rather than entering the bloodstream in meaningful amounts, it carries fewer systemic concerns than acid-suppressing medications.
Who Should Be Cautious
The sodium content in Gaviscon is worth paying attention to if you’re on a sodium-restricted diet, such as for high blood pressure or heart failure. At 52 mg of sodium per tablespoon in the US regular-strength formula, occasional use is unlikely to be a problem, but frequent daily dosing adds up. People with kidney disease should also check with a pharmacist before using it, since the magnesium and aluminum in some formulations can accumulate when kidney function is impaired.
Timing Around Other Medications
Gaviscon can interfere with how your body absorbs other medications. The gel and antacid components can bind to certain drugs in the stomach, reducing how much actually reaches your bloodstream. The general rule is to leave a two-hour gap before or after taking Gaviscon if you also take any of the following:
- Thyroid medication (levothyroxine)
- Certain antibiotics (quinolones and tetracyclines)
- Iron supplements
- Beta blockers for heart conditions
- Bisphosphonates for osteoporosis (such as alendronic acid)
- Antifungal medications
- Steroids for inflammatory conditions
- Antihistamines
This two-hour window gives the other medication enough time to be absorbed before the Gaviscon coating forms, or lets the raft dissipate before you introduce a drug that could get trapped in it. If you take multiple daily medications, the easiest approach is to take Gaviscon after meals and at bedtime, and schedule your other pills for different times.