Alka-Seltzer tablets are effervescent, over-the-counter tablets that dissolve in water to relieve headaches, body aches, heartburn, acid indigestion, and upset stomach. Each original tablet contains three active ingredients: 325 mg of aspirin, 1,000 mg of citric acid, and 1,916 mg of sodium bicarbonate (baking soda). When dropped into a glass of water, the tablet fizzes, breaks apart, and creates a drinkable solution that gets absorbed faster than a standard pill you’d swallow whole.
How the Fizzing Works
The signature fizz is a chemical reaction between two of the tablet’s ingredients: citric acid and sodium bicarbonate. While the tablet is dry, these compounds sit side by side doing nothing. The moment they hit water, both dissolve and their molecules begin colliding, producing carbon dioxide gas, which is the visible bubbling. The reaction also creates sodium citrate, a compound that helps neutralize excess stomach acid.
This effervescence isn’t just for show. It breaks the tablet into tiny particles suspended throughout the water, so the active ingredients reach your stomach already dissolved rather than as a solid chunk that needs to break down on its own. That’s the main advantage of the format over a traditional tablet or capsule.
What Each Ingredient Does
The aspirin in Alka-Seltzer is the same pain reliever found in a standard aspirin tablet, at the same 325 mg dose. It reduces pain, inflammation, and fever. The sodium bicarbonate and citric acid work together as an antacid, neutralizing stomach acid to ease heartburn, sour stomach, and indigestion. This combination is what makes the original formula a two-in-one product: pain relief plus digestive relief in a single dose.
Because of this dual action, Alka-Seltzer is specifically marketed for situations where digestive discomfort overlaps with pain, like an upset stomach paired with a headache, or the general misery after eating and drinking too much.
Different Versions on the Shelf
The original effervescent tablet is the classic product, but the Alka-Seltzer brand now covers a wide range of formulas with different ingredients. Knowing which one you’re picking up matters, because they don’t all contain the same drugs.
- Original: Aspirin, citric acid, and sodium bicarbonate. Treats pain plus stomach issues.
- Heartburn Relief / Gold: Swaps out the aspirin for calcium carbonate, keeping citric acid and sodium bicarbonate. Some versions add simethicone to relieve gas and bloating. These are aspirin-free, purely antacid products.
- Hangover Relief: Contains aspirin and caffeine but no antacid. Designed for headache and fatigue rather than stomach acid.
- Alka-Seltzer Plus (Cold and Flu): A completely different category. These are cold and flu medications in capsule or tablet form, with decongestants, antihistamines, or cough suppressants depending on the variety.
If you’re looking for stomach relief without a pain reliever, the heartburn or gold versions are the right pick. If you need pain relief and don’t have stomach issues, plain aspirin or another pain reliever would do the same job for less money.
Dosage for the Original Formula
The standard dose for adults and children 12 and older is two tablets dissolved fully in a glass of water, taken every four to six hours as needed. You should not exceed eight tablets in a 24-hour period. For adults 60 and older, the maximum drops significantly to just four tablets per day, because older adults face higher risks from both aspirin and the sodium content.
Always dissolve the tablets completely before drinking. Taking them without water or swallowing them dry defeats the purpose of the effervescent design and can irritate your throat and stomach.
Sodium Content and Who Should Be Careful
One detail that catches many people off guard is how much sodium each tablet contains: 567 mg. A standard two-tablet dose delivers over 1,100 mg of sodium, which is nearly half the daily recommended limit of 2,300 mg. If you’re managing high blood pressure, heart failure, kidney disease, or following a low-sodium diet, this is a significant amount that could cause problems.
For occasional use in otherwise healthy people, the sodium is unlikely to be an issue. But if you’re reaching for Alka-Seltzer multiple times a day for several days, sodium intake adds up quickly. People on sodium-restricted diets should check with a doctor before using the original formula.
The Aspirin Risk for Children
Because the original formula contains aspirin, it should never be given to children or teenagers. Aspirin use in young people who have the flu or chickenpox has been linked to Reye’s syndrome, a rare but serious condition that causes swelling in the liver and brain. The Mayo Clinic specifically names Alka-Seltzer as one of the products where aspirin “can show up in some unexpected products,” since many people think of it as an antacid rather than a pain reliever.
This applies to any Alka-Seltzer product that lists aspirin, acetylsalicylic acid, or salicylate in its ingredients. The aspirin-free heartburn versions are not associated with this risk, but it’s worth reading the label carefully to confirm which formula you have at home.
Other Precautions Worth Knowing
Since the active pain reliever is aspirin, all the standard aspirin warnings apply. People with stomach ulcers or bleeding disorders should avoid it. If you’re already taking a blood thinner or another anti-inflammatory pain reliever, adding Alka-Seltzer stacks those effects and raises the risk of stomach bleeding. Drinking alcohol while using any aspirin-containing product also increases that risk.
Alka-Seltzer can interact with a number of prescription medications, particularly blood pressure drugs, diabetes medications, and other blood thinners. If you take daily prescriptions, it’s worth checking for interactions before using it regularly, even though it’s sold over the counter.