Several medicines can help with diarrhea, and the right choice depends on what’s causing it and how long it’s lasted. For a typical bout of acute diarrhea from a stomach bug or something you ate, over-the-counter options like loperamide and bismuth subsalicylate are the most widely used treatments. Chronic or recurring diarrhea sometimes requires prescription medications that target the underlying cause.
Loperamide: The Most Common OTC Option
Loperamide (sold as Imodium and store-brand equivalents) works by slowing down the movements of your intestines. This gives your body more time to absorb water from the food passing through, which firms up your stool and reduces the frequency of bathroom trips.
The standard adult dose is 4 mg (two capsules or tablets) after your first loose bowel movement, then 2 mg after each subsequent loose stool. You should not exceed 8 mg in a 24-hour period with the OTC tablet form, or 16 mg with the capsule form. Most people notice improvement within a few hours.
Loperamide is effective for garden-variety diarrhea, but there are situations where you should not use it. The FDA specifically warns against taking it if you have bloody stools with a high fever (signs of dysentery), if you’re experiencing diarrhea caused by certain bacterial infections like Salmonella or Shigella, or if diarrhea started after a course of antibiotics. In these cases, slowing down your gut can actually trap the infection inside and make things worse. It’s also not recommended for infants under 24 months.
Bismuth Subsalicylate for Milder Symptoms
Bismuth subsalicylate (the active ingredient in Pepto-Bismol and Kaopectate) takes a different approach. Rather than slowing intestinal movement, it reduces the amount of fluid your intestines secrete and has mild antimicrobial properties. It also helps with the nausea and stomach upset that often accompany diarrhea, making it a good choice when you’re dealing with multiple symptoms at once.
This medication should not be used in children younger than 12. Because it contains a compound related to aspirin, it carries a risk of Reye’s syndrome in children and teenagers who have or are recovering from the flu or chickenpox. Children are also more sensitive to its effects, especially if they’re already dehydrated from vomiting or diarrhea. For adults, it’s generally well tolerated, though it can temporarily turn your tongue and stool black, which is harmless.
Oral Rehydration: Not a Medicine, but Essential
The biggest danger from diarrhea isn’t the diarrhea itself; it’s the water and electrolytes you lose. Oral rehydration solutions (sometimes called ORS) contain a precise balance of salts and glucose that helps your body absorb fluid far more efficiently than water alone. The World Health Organization considers ORS one of the most important treatments for diarrhea across all age groups, effective in all but the most severe cases of dehydration.
You can find commercial rehydration drinks like Pedialyte or Drip Drop at most pharmacies. For mild cases, diluted fruit juice, broth, or sports drinks can also help, though they aren’t as precisely balanced. Signs that dehydration is becoming serious include extreme thirst, dark urine, dizziness, and skin that stays pinched up when you pull it. In infants, watch for no wet diapers for three or more hours, no tears when crying, or unusual drowsiness.
Probiotics as a Supporting Treatment
Certain probiotic strains can shorten the duration of acute diarrhea, particularly when it’s caused by a virus. The strains with the strongest evidence are Lactobacillus GG (often labeled LGG), Lactobacillus reuteri, and a beneficial yeast called Saccharomyces boulardii. These appear to work by boosting your immune response in the gut rather than directly fighting the pathogen.
Probiotics are not a replacement for loperamide or rehydration. Think of them as a supplement that may help you recover a day or so faster. The evidence is strongest in children with viral diarrhea (particularly rotavirus). For adults, results are more mixed, but the risk of side effects is very low, so many people find them worth trying. Look for products that list one of those specific strains on the label rather than a generic “probiotic blend.”
Prescription Medicines for Persistent Diarrhea
When diarrhea doesn’t respond to OTC treatments or keeps coming back, a doctor may prescribe something targeted to the cause.
Diphenoxylate with atropine is a stronger prescription version of the same basic approach as loperamide: it slows gut motility. It’s used alongside fluid replacement for diarrhea that’s more severe than what OTC options can manage. Like loperamide, it should not be used when diarrhea involves bloody stool, fever, or is linked to antibiotic use.
Antibiotics like rifaximin are prescribed when diarrhea is caused by a specific bacterial infection or in conditions like traveler’s diarrhea. Your doctor would typically need a stool test to determine whether bacteria are the culprit before prescribing these.
For people with chronic, watery diarrhea that doesn’t have an obvious infectious cause, bile acid malabsorption is an underdiagnosed possibility. Excess bile acids in the colon irritate the lining, triggering it to release extra fluid and speeding up the muscle contractions that push stool through. This causes frequent, urgent diarrhea and cramping. Medications called bile acid binders, most commonly cholestyramine and colestipol, work by trapping bile acids in the intestine before they can cause irritation. These are the first-line treatment for this condition, and many people notice a dramatic improvement.
When OTC Medicines Aren’t Enough
Most acute diarrhea resolves within a day or two. But certain patterns signal that you need more than a trip to the pharmacy. For adults, those include diarrhea lasting more than two days, a high fever, six or more loose stools per day, severe abdominal or rectal pain, and stool that is black, tarry, or contains blood or pus. Any signs of dehydration (dizziness, very dark urine, extreme thirst, sunken eyes) also warrant prompt attention.
The threshold is lower for children. Diarrhea lasting more than a single day, any fever in infants, or a child refusing to eat or drink for more than a few hours all call for a doctor’s evaluation. Infants under 12 months, premature babies, and children with existing medical conditions need especially close monitoring. People who are pregnant, over 65, immunocompromised, or currently taking antibiotics should also stay in closer contact with their doctor if diarrhea develops.