Tums typically provide heartburn relief for about 30 to 60 minutes. That’s significantly shorter than other over-the-counter options, but the tradeoff is speed: Tums start working almost immediately after you chew them, while stronger acid-reducing medications can take an hour or more to kick in.
How Tums Work
The active ingredient in Tums is calcium carbonate, which directly neutralizes the hydrochloric acid in your stomach. When the calcium carbonate meets stomach acid, it produces calcium chloride, water, and carbon dioxide gas (which is why you might burp after taking them). This is a straightforward chemical reaction, not a process that requires absorption into your bloodstream, which is why relief comes so quickly.
The catch is that once the calcium carbonate is used up, there’s nothing left to keep working. Your stomach continues producing acid at its normal rate, and without more antacid to neutralize it, symptoms can return. This is fundamentally different from medications that reduce acid production at the source.
The Acid Rebound Problem
Tums have a quirk that can make them feel like they stop working even sooner than expected. Calcium carbonate triggers what’s called acid rebound: after the initial neutralizing effect wears off, your stomach actually produces more acid than it did before you took the tablet. Research published in the New England Journal of Medicine found that calcium carbonate reliably induced this rebound acid production, and the effect was especially pronounced when food was also in the stomach.
A study in the American Journal of Therapeutics confirmed this pattern. After subjects took calcium carbonate, their stomach pH often dropped back to or below the levels seen with a placebo. In other words, Tums can temporarily make your stomach more acidic than it was before you took them. This doesn’t happen with every person or every dose, but it’s a well-documented effect that helps explain why heartburn sometimes comes roaring back shortly after Tums seem to wear off.
Tums vs. Longer-Lasting Options
If 30 to 60 minutes of relief isn’t cutting it, the next step up is an H2 blocker like famotidine (sold as Pepcid). These take about an hour to start working, but they reduce acid production for 4 to 10 hours. The tradeoff is clear: Tums are faster, H2 blockers last longer. Some people take a Tums for immediate relief while waiting for an H2 blocker to take effect.
Proton pump inhibitors are the strongest over-the-counter option and can suppress acid for a full 24 hours, but they’re designed for daily use over a course of two weeks rather than on-demand relief. They’re not a substitute for Tums in the moment, because they take one to four days of consistent use to reach full effect.
How Many You Can Take
For extra-strength Tums (750 mg calcium carbonate per tablet), the limit is 9 tablets in 24 hours. If you’re pregnant, that drops to 6 tablets in 24 hours. These limits exist partly because of how much calcium you’d be consuming. Exceeding them regularly can lead to elevated calcium levels in your blood and other complications, especially kidney problems.
If you find yourself reaching for Tums multiple times a day, most days of the week, that’s a signal your heartburn needs a different approach. Frequent use also increases your exposure to that acid rebound cycle, potentially creating a pattern where each dose wears off and leaves you feeling worse.
Shelf Life of Tums
Tums are stamped with an expiration date, which is the manufacturer’s guarantee that the tablets will work at full strength until that point. Solid tablets like Tums hold up better over time than liquid antacids, which break down more quickly after expiration. That said, the longer past the expiration date, the less reliable the active ingredient becomes. If your Tums look discolored, crumble unusually, or smell off, toss them regardless of the printed date.
Getting the Most Out of Each Dose
Chew Tums thoroughly before swallowing. The more surface area exposed to your stomach acid, the faster and more completely the reaction happens. Taking them on a completely empty stomach may give you a shorter window of relief, since there’s less material in the stomach to buffer the acid rebound effect. Taking them right after a meal, when heartburn is actively flaring, tends to provide the most noticeable relief, though the rebound effect is also stronger with food present.
Drinking a large glass of water with Tums can dilute stomach acid further in the short term, but it also speeds up how quickly the dissolved calcium carbonate moves out of your stomach, potentially shortening the duration. A small sip to help swallow is fine. Timing matters more than anything: Tums are best used for occasional, short-lived episodes of heartburn rather than as a strategy for managing chronic acid reflux throughout the day.