Alka-Seltzer Original can help with an upset stomach, but it is not designed to treat diarrhea and has no ingredients that address loose stools. The product is indicated for heartburn, acid indigestion, and general stomach discomfort. If diarrhea is your main symptom, a different over-the-counter product will serve you better.
What Alka-Seltzer Actually Does
Each effervescent tablet contains three active ingredients: sodium bicarbonate (1,916 mg), citric acid (1,000 mg), and aspirin (325 mg). When dissolved in water, the sodium bicarbonate and citric acid work together as an antacid, neutralizing excess stomach acid within about 15 minutes. The relief typically lasts one to three hours. The aspirin component acts as a pain reliever, which can help if your upset stomach comes with a headache or general achiness.
That combination makes Alka-Seltzer effective for the burning, bloated, overly acidic feeling you get after eating too much or eating something that disagrees with you. It does nothing, however, to slow intestinal movement, absorb excess fluid in the gut, or fight the bacteria and viruses that commonly cause diarrhea.
Why It Could Make Diarrhea Worse
The aspirin in Alka-Seltzer is actually a concern when your stomach is already irritated. Aspirin is a nonsteroidal anti-inflammatory drug (NSAID) that can increase the risk of bleeding in the stomach and digestive tract. The FDA has specifically warned that aspirin-containing antacid medicines can contribute to serious bleeding events. If your upset stomach involves inflammation of the stomach lining, cramping, or diarrhea, adding aspirin to the mix may irritate things further rather than calm them down.
You’re at higher risk for these bleeding complications if you are 60 or older, have a history of stomach ulcers, take blood-thinning medications, use other NSAIDs like ibuprofen, or drink three or more alcoholic beverages a day. Warning signs of digestive tract bleeding include feeling faint, vomiting blood, black or bloody stools, and stomach pain that worsens rather than improves.
What Works Better for Diarrhea
Two over-the-counter ingredients are actually formulated to treat diarrhea:
- Loperamide (sold as Imodium) slows the speed at which food and fluid move through your intestines, giving your body more time to absorb water. This reduces the frequency of loose stools and helps them become more formed.
- Bismuth subsalicylate (sold as Pepto-Bismol and Kaopectate) works differently. It balances fluid movement in the intestines, reduces inflammation, and prevents diarrhea-causing bacteria and viruses from multiplying in the stomach and gut. This one also treats nausea and general stomach upset, making it the better choice if you have both an upset stomach and diarrhea at the same time.
If your main complaint is acid-related discomfort with no diarrhea, Alka-Seltzer is a reasonable short-term option. If diarrhea is part of the picture, bismuth subsalicylate covers both symptoms in a single product without the aspirin-related risks to your digestive tract.
Sodium Content Worth Knowing About
Each Alka-Seltzer tablet contains nearly 2 grams of sodium bicarbonate, and the standard dose is two tablets. That’s a significant amount of sodium, especially if you’re watching your salt intake due to high blood pressure, heart disease, or kidney problems. For comparison, the American Heart Association recommends no more than 2,300 mg of total sodium per day. A single two-tablet dose of Alka-Seltzer delivers a large portion of that limit before you’ve eaten anything.
Not Safe for Children or Teens
Because Alka-Seltzer contains aspirin, it should never be given to children or teenagers. Aspirin use in young people who have a viral illness, particularly 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 places.” If a child has an upset stomach or diarrhea, stick with age-appropriate remedies and oral rehydration solutions.
Choosing the Right Product
The Alka-Seltzer brand has expanded well beyond the original effervescent tablets. Some products in the line are aspirin-free antacid chews, while others target cold and flu symptoms. The names can be confusing, so always check the active ingredients on the back of the box rather than relying on the brand name alone. If you see aspirin listed, you’re getting a pain reliever along with your antacid, which may or may not be what you need.
For a straightforward upset stomach caused by too much acid, an antacid-only product (with no aspirin) is the gentler choice. For diarrhea, skip the Alka-Seltzer aisle entirely and look for loperamide or bismuth subsalicylate. And if both symptoms persist beyond a couple of days, that’s worth a conversation with your doctor.