The most widely used medicine for diarrhea is loperamide (sold as Imodium), an over-the-counter drug that slows gut movement and reduces the urgency to go. For most adults with a short bout of loose stools, loperamide or bismuth subsalicylate (Pepto-Bismol) will do the job. But the right choice depends on the cause, how severe it is, and whether you’re treating an adult or a child.
Over-the-Counter Options
Loperamide works by binding to receptors in the gut wall that control how fast your intestines push food through. It slows that movement down, gives your intestines more time to absorb water, and tightens the anal sphincter to reduce urgency and accidents. The standard adult dose is two capsules (4 mg) to start, then one capsule (2 mg) after each loose stool, up to a maximum of 16 mg (eight capsules) per day. Most people feel improvement within a few hours.
Bismuth subsalicylate takes a different approach. Rather than slowing gut movement, it reduces inflammation and has mild antibacterial effects in the intestines. It’s a good option for milder diarrhea, especially when nausea or an upset stomach is part of the picture. One harmless but startling side effect: it can turn your tongue dark and your stools grayish black. Both go away once you stop taking it. Because it contains a compound related to aspirin, it should not be given to children or teenagers with flu or chickenpox symptoms due to the risk of Reye’s syndrome.
When You Need a Prescription
Antibiotics are not needed for most diarrhea, which tends to be viral and self-limiting. They become relevant when a bacterial infection is the likely cause, particularly with traveler’s diarrhea picked up abroad. The CDC uses a practical severity scale to guide treatment: if diarrhea is mild and doesn’t disrupt your day, over-the-counter options are sufficient. If it’s moderate, interfering with your plans, or severe enough to be incapacitating, antibiotics enter the picture.
For traveler’s diarrhea, azithromycin is the preferred first-line antibiotic, especially for severe cases, dysentery (bloody diarrhea), or infections acquired in Southeast Asia where antibiotic resistance is common. Another option, rifaximin, is approved specifically for diarrhea caused by noninvasive strains of E. coli. It stays mostly in the gut rather than being absorbed into the bloodstream, which limits side effects. Both are typically taken for just one to three days.
For people with irritable bowel syndrome with diarrhea (IBS-D), a chronic condition rather than an acute infection, eluxadoline is a prescription medication designed for long-term use. It targets receptors in the gut to reduce contractions and pain without completely stopping things up the way loperamide can.
Rehydration Comes First
No anti-diarrheal medicine replaces the fluids and electrolytes your body is losing. Severe diarrhea, defined as more than 10 bowel movements a day or fluid losses that outpace what you’re drinking, can cause dehydration that becomes life-threatening if ignored. For mild to moderate cases, an oral rehydration solution (water mixed with salts and sugar) is the single most important treatment. For children, it’s even more critical because they dehydrate faster.
What Works for Children
Most over-the-counter anti-diarrheal medications are not recommended for young children. Loperamide labels typically restrict use to children over a certain age, and bismuth subsalicylate carries the Reye’s syndrome concern. The foundation of treatment in kids is oral rehydration.
The World Health Organization recommends zinc supplementation alongside rehydration for children with acute diarrhea: 20 mg per day for 10 to 14 days, or 10 mg per day for infants under six months. Zinc shortens the duration of diarrhea and reduces stool output. In countries where zinc deficiency is common, this intervention has a meaningful impact on outcomes.
A newer medication called racecadotril is available in some countries (though not the U.S.) for children over three months. It works differently from loperamide. Instead of slowing gut movement, it blocks an enzyme in the intestinal lining that drives water and electrolyte secretion into the bowel. The result is less watery stool without the constipation that can follow loperamide. It’s meant to be used alongside oral rehydration, starting after three watery stools within 24 hours, for a maximum of seven days.
Probiotics as a Supporting Treatment
Probiotics won’t stop diarrhea the way loperamide does, but they can shorten how long it lasts. A Cochrane review of clinical trials found that probiotics reduced the average duration of diarrhea by about 30 hours and cut the likelihood of diarrhea persisting past three days by roughly a third. Two strains have the strongest evidence behind them: Saccharomyces boulardii (a yeast) and Lactobacillus rhamnosus GG (a bacterium). In trials, Lactobacillus rhamnosus GG shortened diarrhea duration by about 31 hours on average. Saccharomyces boulardii reduced the risk of diarrhea lasting four or more days by nearly 60%.
These are available over the counter in capsule or powder form. They’re most useful for infectious diarrhea and antibiotic-associated diarrhea, not for chronic conditions like IBS.
When to Avoid Anti-Diarrheal Medication
There are situations where stopping diarrhea with medication can actually cause harm. If you have blood in your stool along with a high temperature, these can be signs of dysentery or an invasive bacterial infection. Using loperamide to slow your gut in this situation can trap the pathogen inside, making things worse. The NHS specifically advises against taking loperamide if you have severe diarrhea after a course of antibiotics, because this pattern may indicate a Clostridioides difficile infection that requires targeted treatment, not symptom suppression.
For adults, diarrhea lasting more than two days without improvement, signs of dehydration (excessive thirst, very dark urine, dizziness, little or no urination), severe abdominal pain, bloody or black stools, or a fever above 102°F (39°C) all warrant medical attention rather than continued self-treatment. For children, the threshold is lower: seek help if diarrhea hasn’t improved within 24 hours, if there are no wet diapers for three or more hours, or if the child shows signs of dehydration like a dry mouth, sunken eyes, or skin that stays pinched when you press and release it.