Each Alka-Seltzer 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). These three compounds work together to relieve pain and neutralize stomach acid, and they’re responsible for the fizzing action the product is known for.
The Three Active Ingredients
Aspirin (325 mg) is a standard-dose pain reliever and anti-inflammatory. At 325 mg per tablet, it’s the same amount found in a single regular-strength aspirin. It handles headaches, body aches, and minor pain.
Citric acid (1,000 mg) serves a dual purpose. It’s one of the two acids that react with the baking soda to create the fizz, and it also helps the tablet dissolve quickly in water. On its own, citric acid has no pain-relieving or antacid properties.
Sodium bicarbonate (1,916 mg) is the antacid component. It neutralizes excess stomach acid, which is why Alka-Seltzer works for heartburn, sour stomach, and acid indigestion. It’s also the largest ingredient by weight, making up more than half of each tablet.
What Happens When It Hits Water
The fizzing isn’t just for show. When you drop a tablet into water, the sodium bicarbonate and the two acids (citric acid and aspirin) undergo a chemical reaction. The acids donate hydrogen ions to the bicarbonate, which briefly forms carbonic acid. Carbonic acid is extremely unstable and immediately breaks apart into water and carbon dioxide gas. Those CO2 bubbles are the fizz you see and hear.
By the time the tablet finishes dissolving, the solution in your glass is chemically different from the dry tablet. It contains primarily sodium citrate (an antacid) and a dissolved form of aspirin called sodium acetylsalicylate. This dissolved form of aspirin enters your bloodstream faster than a standard pill you swallow whole, which is one reason the effervescent format can provide quicker relief.
What It’s Designed to Treat
Alka-Seltzer Original is marketed for a specific overlap: minor pain that comes with stomach discomfort. That includes headaches or body aches paired with heartburn, sour stomach, or acid indigestion. It also works for pain alone, functioning as a standard-dose aspirin delivery system. The antacid component makes it particularly useful when stomach upset accompanies the pain, such as after overeating or drinking alcohol.
The Sodium Factor
One detail that surprises many people is the sodium content. Each tablet contains 1,916 mg of sodium bicarbonate, and a significant portion of that is elemental sodium. The recommended dose is two tablets, which roughly doubles the intake. For context, the American Heart Association recommends no more than 2,300 mg of sodium per day total. A two-tablet dose of Alka-Seltzer contributes a substantial chunk of that limit. If you’re watching your sodium intake for blood pressure or heart health, this is worth knowing.
Aspirin Warnings Worth Knowing
Because Alka-Seltzer contains aspirin, it carries the same safety considerations as any aspirin product. Children and teenagers recovering from chickenpox or flu-like illness should not take it due to the risk of Reye’s syndrome, a rare but serious condition that affects the brain and liver.
Aspirin can also cause stomach bleeding. The risk increases if you’re over 60, have a history of ulcers or bleeding problems, take blood thinners or steroid medications, use other anti-inflammatory drugs like ibuprofen or naproxen, or drink three or more alcoholic beverages a day. Signs of stomach bleeding include feeling faint, vomiting blood, black or bloody stools, and persistent stomach pain.
Some people have aspirin allergies that can trigger hives, facial swelling, wheezing, or in severe cases, shock. If you’ve ever had an allergic reaction to aspirin or another anti-inflammatory pain reliever, Alka-Seltzer Original is not safe for you.
Different Alka-Seltzer Products, Different Ingredients
The Alka-Seltzer brand now covers a wide range of products, and they don’t all contain the same ingredients. The Original formula described here is the only one with all three components: aspirin, citric acid, and sodium bicarbonate. Some versions, like Alka-Seltzer Heartburn Relief, drop the aspirin entirely and contain only citric acid and sodium bicarbonate, making them purely antacid products. Other branded variations target cold and flu symptoms or contain entirely different active ingredients like acetaminophen or antihistamines. Checking the specific product label matters, because the name “Alka-Seltzer” alone doesn’t tell you what’s inside.