Alka-Seltzer and Tums are not the same product. They use different active ingredients, come in different forms, and treat overlapping but distinct sets of symptoms. Both neutralize stomach acid, but Alka-Seltzer contains aspirin (a pain reliever) and sodium bicarbonate, while Tums contains only calcium carbonate. That difference matters more than most people realize, especially if you take either one regularly.
Different Active Ingredients
Tums is straightforward: its only active ingredient is calcium carbonate, a potent and fast-acting antacid. You chew the tablet, it reaches your stomach, and the calcium carbonate neutralizes acid directly. That’s it.
Original Alka-Seltzer is a three-ingredient combination. It contains aspirin, sodium bicarbonate (the same compound as baking soda), and citric acid. You dissolve the effervescent tablets in water before drinking. The sodium bicarbonate handles the acid neutralization, the citric acid creates the fizz, and the aspirin relieves pain. This makes Alka-Seltzer a hybrid product designed for situations where heartburn and pain (like a headache) happen at the same time.
Because Alka-Seltzer contains aspirin, it carries risks that Tums simply doesn’t. Aspirin thins the blood, can irritate the stomach lining, and isn’t safe for children or people on blood-thinning medications. If all you need is acid relief, Alka-Seltzer gives you a pain reliever you didn’t ask for.
How Each One Neutralizes Acid
Both products raise the pH of your stomach contents, reducing acidity. An antacid that raises stomach pH from 1.5 to 3.5 produces a 100-fold reduction in acid concentration, which is enough to relieve most heartburn symptoms. But the two compounds get there differently.
Sodium bicarbonate reacts almost instantly with stomach acid, producing carbon dioxide gas and salt. That rapid reaction is why Alka-Seltzer works quickly, but it’s also why it causes belching and a feeling of stomach distention. The fizz isn’t just for show.
Calcium carbonate is also fast-acting and potent, but it has an interesting quirk. It triggers the release of a hormone called gastrin in the lower part of the stomach, which can actually stimulate more acid production after the initial relief wears off. This rebound effect is mild for occasional use but worth knowing about if you reach for Tums multiple times a day.
Neither product lasts very long. Taken on an empty stomach, antacids generally provide about 30 minutes of buffering. After a full meal, they can work for up to 3 hours because food slows stomach emptying.
Speed of Relief
Alka-Seltzer has a slight edge in how fast you feel it working. Because you dissolve it in water first, it arrives in your stomach as a liquid solution, and liquid antacids tend to provide faster relief than tablets you have to chew and swallow. Sodium bicarbonate also reacts with acid nearly instantaneously once contact is made.
Tums isn’t far behind. Calcium carbonate is classified as fast-acting, and most people feel improvement within a few minutes of chewing a tablet. The practical difference in onset between the two is small for most people.
Sodium Content in Alka-Seltzer
This is one of the biggest differences between the two products, and it’s easy to overlook. Each Alka-Seltzer tablet contains 567 milligrams of sodium. A standard dose is two tablets, which means a single dose delivers over 1,100 milligrams of sodium, roughly half of the daily recommended limit for most adults.
The product label warns people with high blood pressure, heart disease, liver cirrhosis, or kidney disease to consult a doctor before use. Anyone on a sodium-restricted diet should take this seriously. Sodium bicarbonate can raise blood pressure and increase the risk of fluid retention and swelling, particularly in people with heart failure or liver disease.
Tums contains no significant sodium, which makes it a much safer choice for people watching their salt intake or managing cardiovascular conditions.
Calcium and Kidney Stone Risk
Tums has its own concern for heavy users: calcium. A single Tums tablet contains between 650 and 1,250 milligrams of calcium depending on the strength, and the maximum daily dose is 15 tablets (10 if you’re pregnant). That’s a lot of calcium.
Kaiser Permanente’s dietary guidance for kidney stone prevention specifically flags calcium-containing antacids like Tums as a risk factor. Taking them between meals or exceeding 1,200 milligrams of calcium per day from antacids can increase the likelihood of developing calcium-based kidney stones. If you have a history of kidney stones, this is worth discussing with your doctor before making Tums a regular habit.
The label also notes that you shouldn’t use the maximum dosage for more than two weeks without medical supervision, and symptoms lasting beyond two weeks warrant a checkup regardless of which antacid you prefer.
Side Effects Compared
The side effect profiles reflect the different ingredients. Alka-Seltzer’s main issues stem from sodium bicarbonate and aspirin:
- Gas and bloating from carbon dioxide production in the stomach
- Fluid retention and swelling due to high sodium content
- Stomach irritation or bleeding risk from aspirin
- Electrolyte imbalances with frequent or high-dose use
In rare cases, taking sodium bicarbonate in very high doses has led to stomach rupture and serious electrolyte disturbances. Sodium bicarbonate that isn’t fully dissolved before drinking also poses risks. During pregnancy, it’s considered possibly unsafe because of concerns about fluid retention and pH imbalances.
Tums side effects are generally milder. Constipation is the most common complaint. The acid rebound effect mentioned earlier can create a cycle where you feel temporary relief followed by a return of symptoms, prompting another dose. Over time, excessive calcium intake can lead to elevated calcium levels in the blood, which brings its own set of complications.
Which One to Choose
If your only symptom is heartburn or acid indigestion, Tums is the simpler and generally safer option. It does one thing (neutralize acid) without adding aspirin or a large sodium load to the equation.
Alka-Seltzer makes more sense when you’re dealing with heartburn alongside a headache or body aches, since the aspirin component addresses pain that Tums can’t touch. But treat it as a combination medication, not just an antacid. If you wouldn’t otherwise take aspirin, you probably don’t need it dissolved in your heartburn remedy.
For people with high blood pressure, heart disease, or kidney problems, the choice leans heavily toward Tums or another low-sodium antacid. For people with a history of kidney stones, neither product is ideal for regular use, but the calcium in Tums is the more relevant concern. In both cases, frequent heartburn that requires daily antacid use points to something worth investigating beyond the medicine cabinet.