Diarrhea, or loose bowel movements, can occur for many reasons. Food poisoning and infections are the most common causes of acute (short-lived) diarrhea. Chronic diarrhea may be caused by ongoing illnesses of the digestive tract, such as inflammatory bowel disease and irritable bowel syndrome.

Conventional treatment for diarrhea involves addressing the cause, if possible, and, in some cases, treating symptoms with medications that slow down the action of the digestive tract.

Supplements called probiotics have shown considerable promise for safely preventing or treating various kinds of diarrhea. The following section summarizes much of the evidence regarding this treatment. For more information, see the full Probiotics article.

Probiotics

Certain bacteria and fungi play a helpful role in the body. For this reason, they are known collectively as probiotics (literally, "pro life"). Some of the most common include the yeast Saccharomyces boulardii and the following bacteria:

  • Lactobacillus acidophilus
  • L. bulgaricus
  • L. reuteri (often studied in the proprietary form Lactobacillus GG)
  • L. plantarum
  • L. casei
  • B. bifidus
  • Saccharomyces salivarius
  • Streptococcus thermophilus

The digestive tract is like a rain forest ecosystem, with billions of bacteria and yeasts instead of trees and frogs. Some of these internal inhabitants are more helpful to your body than others. Probiotics not only help digestive tract function, they also reduce the presence of less healthful organisms by competing with them for the limited available space. For this reason, use of probiotics can help prevent infectious diarrhea.

Antibiotics being taken to treat an infection can disturb the balance of the "inner ecosystem" by killing friendly bacteria. When this occurs, harmful bacteria and yeasts can move in and flourish, which can lead to diarrhea. Probiotic therapy may help prevent this problem. Probiotics also appear to be helpful for preventing or treating forms of diarrhea with different causes.

Traveler's Diarrhea

According to some but not all studies, it appears that regular use of various probiotics can help prevent traveler's diarrhea, an illness caused by eating contaminated food, usually in developing countries.2-7,76

For example, one double-blind, placebo-controlled study followed 820 people traveling to southern Turkey and found that use of a probiotic called Lactobacillus GGsignificantly protected against intestinal infection.53

An even larger double-blind, placebo-controlled study found benefits from using the yeast product S. boulardii.55 This trial enrolled 3,000 Austrians traveling to a variety of countries. The greatest benefits were seen in travelers who visited North Africa and Turkey. The researchers noted that the benefit depended on consistent use of the product, and that a dosage of 1,000 mg daily was more effective than 250 mg daily.

Substances called prebiotics are thought to enhance the growth of probiotics. On this basis, a prebiotic called fructo-oligosaccharides(FOS) has been suggested for preventing traveler’s diarrhea. However, in a 244-participant, double blind study, FOS at a dose of 10 g daily offered only minimal benefits.67

Infectious Diarrhea

Children frequently develop diarrhea caused by infectious viruses. Probiotics may help prevent or treat this condition and may also be useful for viral diarrhea in adults.

A 2001 review found 13 double-blind, placebo-controlled trials on the use of probiotics for acute infectious diarrhea in infants and children. Ten of these trials involved treatment, and three involved prevention.28Benefits have been seen in subsequent studies as well, including one that included almost 1,000 infants.60 Overall, the evidence strongly suggests that use of probiotics can significantly reduce the severity and duration of diarrhea and perhaps help prevent it.

Another, more recent review of 63 trials involving over 8,000 people (mainly infants and children) found that probiotics reduced how long the episode of diarrhea lasted.90 The authors concluded, however, that more research needs to be done to determine which probiotics work best for infectious diarrhea.

In a subsequent smaller review focusing on persistent diarrhea (lasting for 2 weeks or longer), researchers concluded that probiotics are capable of reducing both the duration of the diarrhea episode as well as the stool frequency.91 Another study that was part of this same review suggested that probiotics may help to reduce how long a child is hospitalized due to diarrhea.

One double-blind, placebo-controlled trial of 269 children (ages 1 month to 3 years) with acute diarrhea found that those treated with Lactobacillus GGrecovered more quickly than those given placebo.8 The best results were seen among children with rotavirus infection. (Rotavirus can cause severe diarrhea in children.) In another double-blind, placebo-controlled study, Lactobacillus GGhelped prevent diarrhea in 204 undernourished children.9 In addition to Lactobacillus GG, the probiotics B. bifidum, S. thermophilus, L. casei, L. reuteri, S. boulardii, and Escherichia coli Nissle (a safe strain of E. coli) have also shown promise for preventing or treating diarrhea in infants and children.28,68-69,83,84,94

L. reuterireduced the frequency, duration, and relapse rate of acute diarrhea compared to placebo in a randomized trial of 74 children receiving oral rehydration solution for mild to moderate dehydration.97

Prophylactic use of probiotics was found to be effective at preventing C. difficile -induced diarrhea in a review of 20 randomized trials with 3,421 patients (including three trials with 605 children) when compared to placebo or no treatment. The most effective probiotics were S. boulardii and L. acidophilus combined with L. casei.96However, probiotic therapy is probably not helpful for acute, severe, dehydrating diarrhea.10,80 Keep in mind that diarrhea in young children can be serious. If it persists for more than a couple of days or is extremely severe, it would be wise to contact the child’s physician.

In addition, a large (211-participant), double-blind, placebo-controlled study found that adults with infectious diarrhea can also benefit from probiotic treatment.1

Antibiotic-related Diarrhea

The results of most (but not all) double-blind and open trials suggest that probiotics, especially S. boulardii and Lactobacillus GG, may help prevent or treat antibiotic-related diarrhea (including the most severe form, Clostridium difficlediarrhea).11-19,61,62,70,75, 77,79,84,88-89,92

One study found Lactobacillus rhamnosuseffective in children,81 and another study found that L. caseiwas effective in hospitalized patients. A review of 16 randomized trials also found evidence that probiotics may prevent antibiotic-related diarrhea.93 This review included many different strains of probiotics (eg, Lactobacilli, Lactococcus, Bifidobacterium), which were used alone or in combination. Bacteria that appeared to lack evidence of benefit included Lactobacillus rhamnosus, Lactobacillus sporogenes, Bifidobacterium lactis, and Streptococcus thermophilus. Like the earlier review, the pooled results of 34 randomized trials also found evidence to support the use of probiotics for the prevention of antibiotic-associated diarrhea in both children and adults. Like the earlier review, the pooled results of 34 randomized trials also found evidence to support the use of probiotics for the prevention of antibiotic-associated diarrhea in both children and adults.95

It is sometimes said that it is useless to begin probiotic treatment until after the antibiotics are finished. However, evidence appears to indicate that it is better to begin treatment with probiotics along with the initial use of antibiotics, then continue probiotic treatment for a week or two afterwards.

Note: Diarrhea that occurs in the context of antibiotics may be dangerous. Be sure to talk to your doctor.

Inflammatory Bowel Disease

Crohn’s disease and ulcerative colitis fall into the family of conditions known as inflammatory bowel disease. Chronic diarrhea is a common feature of these conditions.

A double-blind trial of 116 people with ulcerative colitis compared a special probiotic treatment using E. colito a relatively low dose of the standard drug mesalazine.26The results suggest that this probiotic treatment might be as effective as low-dose mesalazine for controlling symptoms and maintaining remission. Evidence of benefit was seen in other trials as well.27

Another study found S. boulardiihelpful for treating diarrhea resulting from Crohn’s disease.24However, two studies failed to find benefit with Lactobacillus probiotics.71-72

Other Forms of Diarrhea

Preliminary evidence suggests that probiotics may be helpful for reducing diarrhea and other gastrointestinal side effects caused by cancer treatment (radiation or chemotherapy).20,21

One study found that S. boulardiican increase the effectiveness of standard treatment for amoebic infections.63

Small, double-blind studies suggest S. boulardii might be helpful for treating chronic diarrhea in people with HIVand hospitalized patients who are being tube-fed.22,23

Premature infants weighing less than 2,500 grams (5.5 pounds) are at risk for a life-threatening intestinal condition called necrotizing enterocolitis (NEC). In a study that pooled the results of 9 randomized, placebo-controlled trials involving 1,425 infants, probiotic supplementation significantly reduced the occurrence of NEC and death associated with it.82A subsequent study found similar benefits in very low birth weight infants weighing less than 1,500 grams (3.3 pounds).87

Irritable Bowel Syndrome (Spastic Colon)

People suffering from irritable bowel syndrome (IBS)experience crampy digestive pain, alternating diarrhea and constipation, and other symptoms. In some people, diarrhea predominates. Although the cause of IBS is not known, one possibility is a disturbance in healthy intestinal bacteria. Based on this theory, probiotics have been tried as a treatment for IBS with diarrhea, but the results have been inconsistent.25

One study tested the potential effectiveness of a Traditional Chinese Herbalremedy for diarrhea-predominant IBS, but failed to find benefit.73