Each Alka-Seltzer Original tablet contains three active ingredients: 325 mg of aspirin, 1,916 mg of sodium bicarbonate (baking soda), and 1,000 mg of citric acid. There are no inactive ingredients in the original formula, which means every milligram of the tablet serves a functional purpose.
The Three Active Ingredients
Aspirin is the pain reliever and fever reducer. At 325 mg per tablet, it’s the same dose you’d find in a single regular-strength aspirin pill. It reduces inflammation and helps with headaches, body aches, and minor pain.
Sodium bicarbonate is ordinary baking soda, and at 1,916 mg it makes up the bulk of each tablet. It neutralizes stomach acid on contact, which is why Alka-Seltzer works for heartburn and upset stomach. It also serves a second purpose: it creates the fizzing reaction that dissolves the tablet in water.
Citric acid (1,000 mg) is the other half of that fizzing reaction. On its own, citric acid is the same compound that makes lemons sour. In the tablet, it reacts with the sodium bicarbonate the moment both hit water.
Why It Fizzes
The effervescence isn’t just for show. When citric acid and sodium bicarbonate meet water, they react to produce sodium citrate, carbon dioxide gas (the bubbles), and water. This reaction dissolves the aspirin completely before you drink it, turning the tablet into a buffered solution rather than a solid pill your stomach has to break down.
That dissolved form makes a real difference in how fast it works. FDA data shows that blood levels of the active pain-relieving compound reach about 29 mg/l within 10 minutes of taking Alka-Seltzer, compared to just 9 mg/l with a standard aspirin tablet at the same time point. At 20 minutes, the gap is still roughly threefold. The buffered solution empties from the stomach faster and gets absorbed more efficiently in the intestines.
Sodium Content Worth Knowing
Because the largest ingredient is baking soda, each tablet contains roughly 489 mg of sodium. A standard dose is two tablets, so that’s nearly 1,000 mg of sodium per dose, close to half the daily recommended limit of 2,300 mg. If you’re watching your sodium intake for blood pressure or heart health, this is a significant amount from a single medication.
The Aspirin Carries Real Risks
Many people think of Alka-Seltzer as an antacid, but it contains a full dose of aspirin. The FDA has specifically warned that aspirin-containing antacid products can cause stomach or intestinal bleeding. The risk is higher if you:
- Are 60 or older
- Have a history of stomach ulcers or bleeding problems
- Take blood thinners
- Take steroid medications
- Take other anti-inflammatory painkillers like ibuprofen or naproxen
- Drink three or more alcoholic drinks daily
Warning signs of internal bleeding include feeling faint, vomiting blood, black or bloody stools, and stomach pain that doesn’t let up. Children and teenagers should not take aspirin-containing products during viral illnesses due to the risk of a rare but serious condition called Reye’s syndrome.
Alka-Seltzer Plus Is a Different Product
The “Plus” versions sold for cold and flu are a separate formulation with additional drugs. Alka-Seltzer Plus Severe Cold and Flu, for example, contains a lower aspirin dose (250 mg) along with three other active ingredients: a cough suppressant, a nasal decongestant, and an antihistamine. These are meant to treat congestion, runny nose, and coughing on top of pain and fever.
The original Alka-Seltzer does none of that. It’s strictly a pain reliever and antacid. If you’re reaching for Alka-Seltzer to treat cold symptoms, you need the Plus line. If you just want relief from a headache, upset stomach, or hangover, the original is the simpler choice with fewer drugs in the mix.
How It Compares to Plain Antacids
Standard antacid tablets (like Tums) contain calcium carbonate and no pain reliever. They neutralize acid but won’t touch a headache. Plain aspirin handles pain but does nothing for heartburn and can actually irritate the stomach lining. Alka-Seltzer bridges both, and because the aspirin is pre-dissolved in a buffered solution, it’s generally less irritating to the stomach than swallowing a dry aspirin tablet. That said, the bleeding risk from aspirin still applies regardless of how it’s delivered.
If your only symptom is heartburn, an antacid without aspirin avoids the bleeding risk entirely. Alka-Seltzer makes the most sense when you’re dealing with both stomach discomfort and pain at the same time.