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Do probiotics cause gas?

Written by the Full Measure editorial team, which sells supplements. Approved for publication by the Full Measure owners. Updated .

Drafted with AI assistance from the sources listed below. How we write these

Quick answer

Yes, they may. NIH says probiotics may cause gas in healthy people and that side effects are usually minor digestive symptoms. In 24 trials in children, adverse events were no more common with probiotics than with control, and gas, bloating, nausea and constipation were among the minor ones. Ask your doctor if symptoms persist.1,2,3

Key facts

  • NIH says that in healthy people probiotics may cause gas, but rarely cause infections or other health problems.1
  • NIH's health professional sheet says the side effects are usually minor, self-limited stomach and bowel symptoms such as gas.2
  • In 24 pediatric trials, 4% of children on probiotics and 6% on control had an adverse event, and the common ones included gas, flatulence, bloating, nausea and constipation.3
  • In a 30 day trial in 100 healthy adults, three single strains and a mix of two caused no change in digestive symptoms or stool compared with placebo.4
  • In a 3 week trial in healthy young adults, stool became looser as the daily dose rose from 100 million to 100 billion CFU.5

What do NIH and NCCIH say about gas from probiotics?

In healthy people, probiotics may cause gas. Side effects are usually minor digestive symptoms that go away on their own.1,2

NIH's consumer sheet puts the same point in plain terms: most probiotics have been used in foods or supplements for decades, they may cause gas in healthy people, and they rarely cause infections or other health problems. NCCIH adds that few studies have looked at probiotic safety in detail, so the real frequency of side effects is not well known.1,6

What do trials show about gas, bloating and loose stools?

The evidence is limited and mixed. In the Cochrane review of pediatric trials, the minor events listed were rash, nausea, gas, flatulence, abdominal bloating and constipation, and overall adverse events were no more common with probiotics than with control. A systematic review of 35 placebo-controlled trials of one Bifidobacterium strain pooled adverse event rates of 15.2% with the probiotic and 14% with placebo, a difference that was not statistically significant.3,7

In a 30 day trial in 100 healthy adults, three single strains and a mix of two of them caused no change in digestive symptoms, bowel movement frequency or stool consistency compared with placebo, and no adverse events were reported.4

In a 3 week trial in healthy young adults, stool became looser as the daily dose of a two-strain mix rose from 100 million to 100 billion CFU, and the high doses were well tolerated.5

Two limits apply. The analysis of one strain, called BB-12, noted that half of its trials gave no adverse event data, and the two trials above enrolled healthy adults, so neither speaks for people with bowel conditions.5,7

How long does gas last after starting a probiotic?

None of the sources we read measured how long gas lasts. A 2021 review of probiotics taken in pregnancy noted that most symptoms after starting a probiotic begin early and taper off with continued use, and NIH describes the symptoms as self-limited. That is a general pattern from reviews, not a promise for any one product.2,8

MedlinePlus explains where gas comes from in general: air that is swallowed, and bacteria in the large intestine breaking down food that was not digested. It adds that foods that cause gas in one person may not in another. The sources do not tell us which of these explains gas after a probiotic.9

Who should ask their doctor about gas after a probiotic?

  • Anyone with a fever, vomiting, bloody diarrhea or severe belly pain should ask a doctor rather than put it down to the probiotic.2
  • People who are seriously ill, in hospital or have a weakened immune system should ask their doctor before taking a probiotic, because NIH says probiotics might cause infections in them.1
  • Anyone whose gas or bloating does not settle, or keeps coming back, should ask their doctor, because the sources describe the usual symptoms as brief.2,9
  • People who take an antibiotic or an antifungal medicine can ask their pharmacist whether it matters for a probiotic.10

Questions people ask

Do probiotics cause gas?

NIH says probiotics may cause gas in healthy people, usually as a minor, self-limited digestive symptom. Ask your doctor if it lasts or comes with fever, vomiting or bloody diarrhea.1,2

Do probiotics cause gas and bloating?

In a Cochrane review of pediatric trials, gas, flatulence and abdominal bloating were among the minor adverse events, and overall adverse events were no more common than with control.3

Do probiotics cause diarrhea?

Diarrhea was among the digestive symptoms reported in trials in pregnant women, and in one trial in healthy young adults stool became looser as the daily dose rose from 100 million to 100 billion CFU. Ask your doctor about any diarrhea with blood or fever.5,8

Do probiotics cause constipation or nausea?

The Cochrane review of pediatric trials listed nausea and constipation among the minor adverse events, at overall rates no higher than with control.3

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Sources

  1. Office of Dietary Supplements, National Institutes of Health. Probiotics: Fact Sheet for Consumers. Updated November 17, 2025. Opened 2026-10-07.
  2. Office of Dietary Supplements, National Institutes of Health. Probiotics: Fact Sheet for Health Professionals. Updated March 25, 2025. Opened 2026-10-07.
  3. Guo Q, Goldenberg JZ, Humphrey C, El Dib R, Johnston BC. Probiotics for the prevention of pediatric antibiotic-associated diarrhea. Cochrane Database Syst Rev (a systematic review of randomized trials). 2019;4(4):CD004827. Opened 2026-10-11.
  4. Plaza-Diaz J, Gomez-Llorente C, Campaña-Martin L, et al. Safety and immunomodulatory effects of three probiotic strains isolated from the feces of breast-fed infants in healthy adults: SETOPROB study. PLoS One. 2013;8(10):e78111. Opened 2026-10-07.
  5. Larsen CN, Nielsen S, Kaestel P, et al. Dose-response study of probiotic bacteria Bifidobacterium animalis subsp lactis BB-12 and Lactobacillus paracasei subsp paracasei CRL-341 in healthy young adults. Eur J Clin Nutr. 2006;60(11):1284-1293. Opened 2026-10-07.
  6. National Center for Complementary and Integrative Health. Probiotics: Usefulness and Safety. Last updated August 2019. Opened 2026-10-07.
  7. Kumar A, Merenstein D, Tan T, Obeng-Nyarkoh PI, Hojsak I, D'Amico F. Safety of One of the Most Commonly Used Probiotic Strains: Systematic Review and Meta-analysis of Reported Adverse Events. Probiotics Antimicrob Proteins. 2026;18(3):4037-4048. Opened 2026-10-11.
  8. Sheyholislami H, Connor KL. Are probiotics and prebiotics safe for use during pregnancy and lactation? A systematic review and meta-analysis. Nutrients. 2021;13(7):2382. Opened 2026-10-07.
  9. MedlinePlus. Gas (flatulence, belching) health topic summary from the National Institute of Diabetes and Digestive and Kidney Diseases. U.S. National Library of Medicine. Opened 2026-10-11.
  10. Office of Dietary Supplements, National Institutes of Health. Dietary Supplements for Immune Function and Infectious Diseases: Fact Sheet for Health Professionals. Updated March 10, 2025. Opened 2026-10-07.

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.