Gaviscon typically provides relief from heartburn and acid reflux for up to 4 hours per dose. In clinical comparisons, 75% of patients experienced relief lasting more than 4 hours with liquid Gaviscon, compared to only 23% getting the same duration from a standard antacid. How long it actually works for you depends largely on when you take it relative to meals.
How Gaviscon Works Differently Than Antacids
Most antacids simply neutralize stomach acid. Gaviscon does something more physical. Its active ingredient, sodium alginate, reacts with your stomach acid to form a gel. Bicarbonate in the formula generates tiny carbon dioxide bubbles that get trapped in the gel, turning it into a foam that floats on top of your stomach contents like a raft sitting on water.
This floating barrier parks itself right at the top of your stomach, blocking acid from splashing up into your esophagus. It also displaces a concentrated pocket of acid that naturally forms near the junction of your stomach and esophagus after eating. Because the raft is physically sitting in your stomach rather than being absorbed into your bloodstream, it can keep working for several hours as long as it stays intact.
Timing Around Meals Changes Everything
The single biggest factor affecting how long Gaviscon lasts is whether you take it with food in your stomach. In a study measuring how quickly Gaviscon empties from the stomach, the results were dramatic. When taken 30 minutes before a meal (on a mostly empty stomach), half the dose cleared in just 21 minutes. When taken 30 minutes after a meal, it took over 3 hours for half the dose to empty. Taking it 2 hours after eating fell somewhere in between, at about 40 minutes.
This makes intuitive sense. Food slows stomach emptying, and the raft needs to stay in your stomach to do its job. Once it passes into the small intestine, the protective barrier is gone. That’s why the standard recommendation is to take Gaviscon after meals and at bedtime, when food is present to anchor the raft in place longer.
How Quickly You’ll Feel Relief
Gaviscon starts working within minutes. The alginate reacts with stomach acid almost immediately, and the raft forms quickly enough to begin blocking reflux right away. Most people notice a reduction in heartburn within 5 to 10 minutes of taking a dose. This fast onset is one reason people reach for it over slower-acting acid reducers, which can take 30 minutes to several hours to kick in.
The tradeoff is that Gaviscon’s relief window is shorter than medications that reduce acid production at the source. Proton pump inhibitors and H2 blockers work for 12 to 24 hours but take longer to start. Gaviscon fills the gap when you need something now.
How Often You Can Take It
The standard adult dose for Gaviscon liquid is 10 to 20 ml (two to four 5 ml spoonfuls) after meals and at bedtime, up to four times a day. Children 12 and over follow the same dosing. This schedule lines up with the roughly 3 to 4 hour effective window, spacing doses so that each meal gets its own protective raft.
If you find yourself needing Gaviscon more than four times a day or relying on it daily for more than two weeks, that’s a signal your reflux may need a different approach. Frequent, persistent heartburn sometimes points to conditions that benefit from longer-acting treatments.
What Shortens or Extends Its Effect
Several factors influence how long your particular dose holds up:
- Meal size and composition. Larger, fattier meals keep food in your stomach longer, which means the raft sticks around longer too. A light snack won’t anchor it as effectively.
- Body position. Lying down after eating can shift how the raft sits relative to your esophagus. Taking Gaviscon at bedtime works well precisely because the raft floats on top of your stomach contents while you’re horizontal.
- Stomach acid levels. The raft needs acid to form properly. If you’re also taking a strong acid-reducing medication, the raft may not gel as effectively, though this combination is still commonly used.
- Formulation differences. Gaviscon Advance contains a higher concentration of alginate than regular Gaviscon, producing a thicker, more durable raft. The version you buy matters.
Spacing Gaviscon Around Other Medications
Because the raft and its antacid components can physically trap other medications and interfere with their absorption, you should leave a 2-hour gap before or after taking Gaviscon if you also use thyroid medications, iron supplements, certain antibiotics (quinolones and tetracyclines), antifungal medications, beta blockers, bisphosphonates for bone health, or steroids. The NHS maintains a full list of affected medications, and the general rule is simple: if you take prescription pills, keep them well separated from your Gaviscon dose.