Alka-Seltzer’s main ingredient is sodium bicarbonate, which is the same compound as baking soda. Each Original tablet contains 1,916 mg of it. But Alka-Seltzer is not just baking soda. It also contains 1,000 mg of citric acid and 325 mg of aspirin, making it a fundamentally different product from the box of baking soda in your kitchen.
What’s Actually in an Alka-Seltzer Tablet
The sodium bicarbonate in Alka-Seltzer is labeled as “heat-treated,” meaning it’s been processed for stability, but chemically it’s the same substance you’d find in Arm & Hammer. It makes up the bulk of each tablet by weight. The citric acid is there to create the fizz: when you drop the tablet in water, the citric acid reacts with the sodium bicarbonate to produce carbon dioxide gas (the bubbles), water, and sodium citrate. That reaction is what dissolves the tablet and delivers the medicine in liquid form.
The aspirin is the part many people don’t realize is there. At 325 mg per tablet, it’s a full-strength aspirin dose, identical to a standard aspirin pill. That means Original Alka-Seltzer is a pain reliever and an antacid combined, not just a stomach settler.
How It Differs From Plain Baking Soda
People have used plain baking soda dissolved in water as a home antacid for generations, and it works. Sodium bicarbonate neutralizes stomach acid on contact. Harvard Health Publishing notes that sodium bicarbonate is the active antacid ingredient in seltzer products like Alka-Seltzer. So if all you want is acid relief, a half teaspoon of baking soda in water does roughly the same job as the antacid portion of Alka-Seltzer.
The key differences are practical. Alka-Seltzer’s effervescent design forces you to dissolve it fully before drinking, which matters for safety (more on that below). The citric acid and sodium bicarbonate react to form sodium citrate, a buffered salt that’s gentler on the stomach than raw baking soda. And the aspirin adds pain relief that plain baking soda can’t provide, which is useful for headaches or body aches but comes with its own risks.
Not All Alka-Seltzer Products Are the Same
The Alka-Seltzer lineup includes several products with very different formulas. Original Alka-Seltzer contains aspirin. Alka-Seltzer Gold, on the other hand, is aspirin-free. It uses a combination of sodium bicarbonate (1,050 mg) and potassium bicarbonate (344 mg) alongside citric acid, and it dissolves into sodium citrate and potassium citrate. It’s a pure antacid with no pain reliever.
Other products in the line, like Alka-Seltzer Plus Cold and Flu, swap the formula entirely and may contain acetaminophen, decongestants, or antihistamines instead of sodium bicarbonate. The name “Alka-Seltzer” on the box doesn’t guarantee baking soda is inside. Check the active ingredients panel.
The Sodium Problem
Because sodium bicarbonate is a sodium salt, Alka-Seltzer delivers a significant dose of sodium with every use. A single Alka-Seltzer Heartburn Relief tablet contains 489 mg of sodium, and the standard dose is two tablets. That’s nearly 1,000 mg of sodium from one dose, close to half of the 2,300 mg daily limit recommended for most adults.
For people with high blood pressure, heart failure, or kidney disease, this is a real concern. Guidelines for people with hypertension suggest staying under 1,500 mg of sodium per day. A single two-tablet dose of Alka-Seltzer can eat up most of that allowance before you’ve had a meal. Plain baking soda carries the same risk, since the sodium comes from the bicarbonate itself.
Stomach Safety With Sodium Bicarbonate
The FDA has documented a specific and serious risk with sodium bicarbonate antacids: stomach rupture. When sodium bicarbonate hits stomach acid, it produces carbon dioxide gas rapidly. If the stomach is already full of food or drink, the added gas can stretch it beyond its limits. The FDA identified 21 cases of stomach rupture linked to sodium bicarbonate ingestion between 1926 and 1993, five of which were fatal.
This applies to both Alka-Seltzer and plain baking soda. The FDA’s proposed labeling warns users to never take the product when overly full from food or drink, and to make sure the tablet is completely dissolved and all bubbling has stopped before drinking. These aren’t suggestions for convenience. They exist to prevent gas from building up too quickly inside the stomach.
Aspirin Risks in Alka-Seltzer Original
The aspirin in Original Alka-Seltzer introduces risks that plain baking soda doesn’t carry. Children and teenagers should never take aspirin-containing products during viral illnesses like the flu or chickenpox, because aspirin use in this age group is linked to Reye’s syndrome, a rare but potentially fatal condition that causes brain swelling and liver damage. The Mayo Clinic specifically names Alka-Seltzer as a product where aspirin “can show up” unexpectedly.
For adults, the aspirin means Alka-Seltzer Original isn’t appropriate as a daily antacid. Regular aspirin use increases the risk of stomach bleeding, and combining it with the sodium bicarbonate in the same tablet doesn’t eliminate that risk. If you’re reaching for Alka-Seltzer purely for heartburn or indigestion, Alka-Seltzer Gold or plain baking soda avoids the aspirin exposure entirely.
When Baking Soda Alone Makes More Sense
If your goal is occasional acid relief and you don’t need pain relief, plain baking soda in water is a cheaper, simpler option. You control the dose, you avoid aspirin, and you skip the citric acid. The tradeoff is that raw baking soda dissolved in water can taste unpleasant and may cause more sudden gas production in the stomach than a buffered effervescent tablet.
Neither option is a good long-term solution for recurring heartburn or indigestion. The sodium load alone makes daily use problematic, and frequent need for an antacid usually signals an underlying issue worth investigating. For occasional use, though, the core ingredient doing the antacid work in Alka-Seltzer is the same compound sitting in your pantry.