Do Probiotics Work? What the Trials Show for IBS, Antibiotics and More

Probiotics are live bacteria or yeasts sold in capsules, powders and foods. Each strain behaves differently, so a result for one product does not carry over to another. This guide is mainly about adults; where a result comes from children, it says so. Results differ by strain, and where trials pooled many strains, we say that.

The short version

• Irritable bowel syndrome (IBS): a few strains, such as certain Escherichia coli and Lactobacillus strains, eased overall symptoms, at low to moderate certainty. C Grade C (Goodoory 2023).
• Diarrhea from antibiotics in adults and children: probiotics (many different strains, pooled) cut C. difficile diarrhea from 3.2% to 1.6%, at low certainty; results differ by strain. C Grade C (Esmaeilinezhad 2025).
• H. pylori treatment: the yeast Saccharomyces boulardii added to antibiotics helped clear the infection slightly more often in adults. B Grade B (Chang 2026).
• Healthy adults: no clear change in gut bacteria diversity against placebo. B Grade B (Kristensen 2016).
• Severely ill people: deaths rose with a multi-strain product against placebo in predicted severe acute pancreatitis. C Grade C for harm in that illness (one large trial, later under an expression of concern), but serious enough to avoid probiotics in a severe attack unless the care team prescribes them; indirect for other severe illness (Besselink 2008; Lancet 2010).

Do probiotics help IBS?

C Grade C: a few strains may help, and most evidence is weak. A 2023 review of 82 trials (10,332 people) found moderate-certainty evidence that certain Escherichia coli strains eased overall IBS symptoms, and low-certainty evidence for Lactobacillus strains, including Lactobacillus plantarum 299v. For belly pain, the evidence was low certainty for Saccharomyces cerevisiae I-3856 and Bifidobacterium strains; for bloating, very low certainty for multi-strain products and Bacillus strains. Side effects were no more common than on placebo (55 trials) (Goodoory 2023).

The American College of Gastroenterology suggests against probiotics for overall IBS symptoms (a conditional recommendation on very low-quality evidence) (ACG 2021; Lacy 2021). The American Gastroenterological Association's review found 44 different probiotics or mixtures tested in IBS, with low overall certainty (Preidis 2020). Our probiotics page shows B for IBS belly pain; at low certainty, these reviews support C. See our IBS protocol.

Do probiotics help bloating?

D Grade D: very weak evidence, and only in people with IBS. The only pooled evidence is in people with IBS, where multi-strain products and Bacillus strains showed a possible benefit; the grade is D because that review rated the evidence very low certainty (Goodoory 2023). The ACG found no type of probiotic helped bloating in its pooled analysis (ACG 2021). There is no good evidence that probiotics ease bloating in people without IBS.

Should you take probiotics with antibiotics?

C Grade C in adults and children, grade B in children alone. A 2025 Cochrane review pooled 38 trials (13,179 people) of any strain or dose, taken with antibiotics, so its result is pooled across strains and products and cannot show which one works. C. difficile diarrhea, a severe gut infection, fell from 3.2% to 1.6% (risk ratio 0.50), and across 40 trials (13,419 people) antibiotic diarrhea fell from 27.4% to 23% (risk ratio 0.67), both at low certainty; 28 of the included studies had links to probiotic companies (Esmaeilinezhad 2025). The AGA's review found the best evidence, still low certainty, for S. boulardii; the 2-strain combination of Lactobacillus acidophilus CL1285 and Lactobacillus casei LBC80R; a 3-strain combination of L. acidophilus, L. delbrueckii subsp. bulgaricus and Bifidobacterium bifidum; and that 3-strain mix plus Streptococcus salivarius subsp. thermophilus. These are the strains with the most trial evidence, not a pick of one product; results differ by strain (Preidis 2020). In children, 33 trials (6,352) found antibiotic diarrhea in 8% on probiotics against 19% on control (moderate certainty), and the authors named high-dose Lactobacillus rhamnosus or S. boulardii products as the ones to confirm (Guo 2019); ask your child's doctor. For the yeast product and for spacing, see S. boulardii for antibiotic-associated diarrhea and can I take probiotics with antibiotics?

After antibiotics, "restoring" your gut is unproven. Grade C. In mice and in people given antibiotics, a multi-strain probiotic delayed the return of the person's own gut bacteria compared with no probiotic (Suez 2018).

Do probiotics help H. pylori treatment?

B Grade B: a small gain. Across 15 trials in adults, adding S. boulardii to H. pylori antibiotics cleared the infection in about 6 more people per 100 (risk ratio 1.07, moderate certainty), and across 11 trials, side effects fell from 36.0% to 19.7% (low certainty) (Chang 2026). Probiotics don't replace the antibiotic course. See H. pylori infection.

Do probiotics help bacterial vaginosis?

B Grade B, as an add-on. Bacterial vaginosis is an imbalance of vaginal bacteria that needs a diagnosis. In 14 trials, adding probiotics to antibiotics cleared it more often than antibiotics alone or with placebo (risk ratio 1.23). In 3 small trials comparing probiotics alone with antibiotics, the results were too uncertain to tell; don't use probiotics instead of prescribed treatment. The authors' plain-language summary says oral Lactobacillus rhamnosus did better than vaginal use, and that results vary with route and dose (Chen 2022). See a clinician for symptoms; see also bacterial vaginosis.

Do probiotics help ulcerative colitis?

C Grade C. In mild to moderate ulcerative colitis, probiotics (single strains and mixtures, pooled) may bring more remission than placebo (risk ratio 1.73; 9 trials, 594 people; low certainty) (Kaur 2020). No single product has been shown to be better than another, and the AGA calls this a knowledge gap (low certainty) (Preidis 2020). The review's 14 trials included 2 in children. Use probiotics only alongside the treatment your gastroenterology team prescribes; see our ulcerative colitis protocol.

Do probiotics help gut health if you're healthy?

B Grade B: no clear change in a healthy gut. Looking at 7 trials in healthy adults, probiotics did not change the diversity or richness of gut bacteria compared with placebo; 1 of the 7 saw a shift in the overall make-up (Kristensen 2016). These trials measured gut bacteria, not health. For constipation, eczema, colds and hay fever, see constipation, eczema, cold and flu season and seasonal allergies.

When is the best time to take probiotics?

There is no good evidence that the time of day, taking them with meals, or refrigerated rather than shelf-stable products change results. In children on antibiotics, the Cochrane review judged that higher-dose products worked better, and noted serious infections in very ill or immunocompromised children, including those with a central line (Guo 2019). Ask your child's doctor before giving any probiotic. With an antibiotic, follow the spacing in can I take probiotics with antibiotics?

What we'd skip

• Any probiotic for overall IBS symptoms without a named, tested strain: most evidence is low certainty, and the ACG suggests against (Goodoory 2023; ACG 2021).
• Probiotics to "reset" your gut after antibiotics: the gut's own bacteria took longer to come back in one small study (Suez 2018).
• Probiotics in severe illness or intensive care, with a central line or with a weak immune system, unless your care team advises them (see Safety).
• Any probiotic for a premature baby, unless the baby's hospital team gives it: the FDA warns of fatal infections and has approved none for infants (FDA 2023).
• S. boulardii for older adults in hospital, especially with a central line or in intensive care; in one hospital series, the authors say older age should rule these products out (Poncelet 2021).

Safety and interactions

• Side effects: in the antibiotic trials, side effects were no more common on probiotics; cramps, nausea, fever, soft stools, wind and taste changes were the usual ones in both groups. This applies to people who are not immunocompromised (Esmaeilinezhad 2025).
• Severe illness: in 296 people with predicted severe acute pancreatitis, a multi-strain probiotic given into the gut twice daily raised deaths to 16% against 6% on placebo, and 9 developed bowel ischaemia (loss of blood flow to the gut) against none (Besselink 2008); the journal later published an expression of concern about the trial (Lancet 2010).
• Bloodstream infections: Lactobacillus bloodstream infections are rare but can be deadly, and they are more common in people taking probiotics; probiotic strains including L. rhamnosus GG and L. plantarum have been matched to the bacteria in patients' blood. Risk factors include severe illness, a weak immune system, intensive care and central venous catheters (Kullar 2023). In a hospital series of 10 adults with yeast fungemia (Saccharomyces in the blood), 6 had been prescribed S. boulardii, 7 had a central line, 3 were in intensive care, and half died; three were aged 80 or older with no intensive care stay or central line, and the authors say older age should rule these products out (Poncelet 2021). In 4 cases, opening packets near patients with catheters may have spread the yeast (Hennequin 2000). Unless your care team advises them, avoid probiotics if you have severe immune suppression, a central line or a critical illness, or are in intensive care; never give one to a premature baby yourself.
• Premature babies: the FDA warned in 2023 that probiotics given to preterm infants in hospital can cause invasive, sometimes fatal infection, including one death that year, and that no probiotic is FDA-approved as a drug for infants (FDA 2023).
• Medicines: antibiotics: see the question page above. Ask your pharmacist about timing with omeprazole or with antifungal medicines such as fluconazole. If you take drugs that weaken the immune system, ask your prescriber first.
• Quality: see how to choose a quality supplement.

When to see a doctor

• Urgently: fever, chills or feeling very unwell while taking a probiotic if you have a central line, a weak immune system or a serious illness (possible bloodstream infection); or severe or bloody diarrhea, fever or belly pain during or after antibiotics (possible C. difficile infection); signs of dehydration (very little urine, dizziness, a dry mouth, or a sunken soft spot on a baby's head); any diarrhea, fever or illness in a baby; in a baby, fewer wet diapers (nappies), any fever in a young baby, or blood in the stool; any new illness if your immune system is weak.
• Soon: diarrhea or bowel symptoms that last more than a few days or keep coming back; blood in your stool or black stools, weight loss, bowel symptoms that start later in life, or a family history of bowel cancer or inflammatory bowel disease; these warning signs call for tests for colon cancer and inflammatory bowel disease (ACG 2021). With IBS and diarrhea, the ACG also suggests tests for coeliac disease (Lacy 2021).
• Vaginal symptoms: unusual discharge, odor or itching need a clinician, especially in pregnancy.

Don't stop a prescribed medicine on your own; ask the prescriber or pharmacist. If you are pregnant or breastfeeding, ask your midwife or obstetric team. If you are under 18, ask a clinician.

FAQ

Do probiotics actually work? For some uses and some strains. Probiotics (many different strains, pooled) cut C. difficile diarrhea during antibiotics at low certainty (grade C), S. boulardii slightly raised H. pylori clearance in adults (grade B), and a few strains may ease IBS (grade C). In healthy adults, they did not change gut bacteria diversity.

What is the best time to take probiotics? There is no good evidence that the time of day or meals matter. With an antibiotic, follow the spacing your pharmacist gives.

Are probiotics safe? For most healthy adults, side effects in trials were no more common than on placebo. People who are severely ill, have a central line or a weak immune system have had serious bloodstream infections, so they should use them only on medical advice, and older adults in hospital, especially with a central line or in intensive care, should avoid S. boulardii. Never give a probiotic to a premature baby yourself; the FDA has approved none for infants.

Do probiotics help bloating? Only very weak evidence, and only in people with IBS (grade D); the ACG found no type of probiotic helped bloating in its pooled analysis.

Related pages

• Probiotics · Lactobacillus acidophilus · Lactobacillus reuteri
• IBS protocol · Antibiotic-associated diarrhea protocol · C. difficile protocol · H. pylori infection · Bacterial vaginosis · Ulcerative colitis protocol
• S. boulardii guide · Probiotics with antibiotics · Constipation
• How we grade

Sources

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