What Are The Side Effects Of Too Much Probiotics?

Too much probiotic produces, at most, a few days of wind, bloating or a softer stool: in the one trial that tested a very high count, 34 healthy adults took 100 billion CFU a day of a single Lactobacillus rhamnosus strain for three weeks with no change in gut symptoms, stool frequency or stool consistency,¹ and across 36 randomised trials in 9,312 adults, adverse events on live cultures were no more common than on placebo (relative risk 1.00).² Starting any new supplement raises questions about dose, side effects and how long results take, so this page sets out what the trials record when the count is high, whether there is a daily maximum, and who the NHS says should talk to a doctor before taking live cultures at all.

No supplement is entirely without risk, but the recorded side effects of live cultures are short-lived gut effects, and the pooled trials put them at placebo rates. Here is why.

What are the side effects of taking too much probiotics?

Live cultures are a food supplement, not a medicine, and the pooled trials record their adverse events at rates no higher than placebo: in the 2025 Cochrane review, 37 trials in 11,911 people taking antibiotics recorded an adverse event in 10.9% of those on live cultures against 12.2% of controls, and the common events in both groups were "abdominal cramping, nausea, fever, soft stools, flatulence, and taste disturbance".³ Taking more than the label dose does not add a new category of risk in the trial record; it may bring these early effects on sooner.

• Mild stomach upset. Cramping, bloating and nausea are the recorded early events.³ They usually pass within a week or two; if they persist, drop back to the label dose or stop, and see a GP if they do not settle.
• Temporary constipation. Constipation was among the common adverse events recorded in the children's antibiotic-course trials, at an overall adverse-event rate of 4% on live cultures against 6% on placebo.⁴ It is usually short-lived; if it continues, reduce the dose.
• Flatulence. Wind and a softer stool are the two events most often reported in the first days, and the ones most likely with a high count.³

These effects belong to the first days of a new course and should not last. If you have allergies, read the ingredients list, since capsules and drinks can carry milk, soya or gluten from the culture medium. If you take regular prescription medicine, a pharmacist can confirm that the two can be taken together.

How many probiotics is too much?

The trials have not found a ceiling. One capsule a day is the usual label dose, and it is the dose to follow, whether the product is made for children, teenagers or adults. The highest count tested for tolerance, 100 billion CFU a day for three weeks, changed nothing on the gut symptom questionnaire or in the stool diary, and left liver and kidney blood tests unchanged.¹ More is not better for most outcomes, either: a 2017 review of dose-response studies found a clear dose-response only for diarrhoea during antibiotics, and none for bowel function, immune markers or general health.⁵ Taking more capsules than the label says is unlikely to harm and unlikely to add anything.

What is the maximum amount of probiotics you can take in a day?

There is no official maximum. Label doses differ by product, species and purpose, so the count on your pack is the one to follow.

• Infants and children. There is no set recommendation for how much a child should take. In the 2019 Cochrane review of 33 antibiotic-course trials in 6,352 children, 5 billion CFU a day or more did better than lower doses (diarrhoea in 8% against 23% on placebo at the higher dose), and none of the 24 trials that reported adverse events found a serious one attributable to the cultures.⁴ Ask a pharmacist or GP before giving any supplement to a child.
• Teenagers and adults. Adult products state their count in billions of CFU per capsule, and one capsule a day is the usual dose. The adult trials ran across a wide range of counts depending on the strain and the outcome, and the tolerance trial above sits at the top of that range at 100 billion a day.^{1, 5}

Can taking probiotics daily be harmful?

The gut houses trillions of microbes, bacteria and fungi among them, and live cultures add specific species to that community for as long as you take them. For most people the NHS says probiotics "appear to be safe", and that if you have a healthy immune system "they shouldn't cause any unpleasant side effects"; if you have an existing health condition or a weakened immune system, it says to talk to a doctor before taking any probiotic supplement.⁶ A 2015 safety review adds the caveat that trials report safety outcomes "inconsistently", and that the serious events described in case reports, such as bloodstream infection, are in susceptible individuals rather than healthy adults.⁷

Live cultures have a shelf life. A good label states the species, the number of live organisms and the date that number is guaranteed to; past that date fewer organisms are live, so check the date and store the product as the pack directs. Taken as the label says, by someone with a healthy immune system, a daily live culture is as safe as the trials above describe.

If you still have questions about safety, the Health Insiders blog has a page on each: can probiotics make you tired?, can probiotics make you anxious? and how long should I take probiotics?

Frequently asked questions

What if I accidentally took two probiotics in one day?

Nothing in the trial record suggests a double dose matters. In a tolerance trial run by the strain's manufacturer, 34 healthy adults took 100 billion CFU a day of a single Lactobacillus rhamnosus strain for three weeks and reported no change in gut symptoms, stool frequency or stool consistency, a count far above two capsules of most products; across 36 randomised trials in 9,312 adults, adverse events on live cultures matched placebo.^{1, 2} Take the next dose as the label says; the most you might notice is some wind or a softer stool that day.

Can too much probiotic cause constipation?

Constipation is recorded among the common adverse events in the children's antibiotic-course trials, alongside rash, nausea, wind and bloating, at an overall rate no higher than placebo.⁴ In adults with constipation the pooled trials run the other way, with stool frequency up. If constipation starts with a new culture and does not pass within a week or two, reduce the dose or stop.

Is 100 billion CFU too much?

Not in the one trial that tested it: 34 healthy adults took that count daily for three weeks with no change in gut symptoms, stool habit or liver and kidney blood tests, and no serious adverse event.¹ It is also more than most outcomes need; the only outcome with a clear dose-response is diarrhoea during antibiotics.^{4, 5}

Can you take probiotics every day?

Yes, for most people. The NHS says probiotics appear to be safe for people with a healthy immune system, and that anyone with an existing health condition or a weakened immune system should talk to a doctor first.⁶ Follow the label dose, usually one capsule a day.

Sources checked on 19 October 2026.

Sources

1. Wind RD, et al. British Journal of Nutrition, 2010 (tolerance and safety of a Lactobacillus rhamnosus strain in healthy volunteers). Randomised double-blind trial, 34 healthy adults, 100 billion CFU a day, 3 weeks; run by the strain's manufacturer. PubMed 20691131.
2. Liao W, et al. Probiotics for the Prevention of Antibiotic-associated Diarrhea in Adults: A Meta-Analysis of Randomized Placebo-Controlled Trials. Journal of Clinical Gastroenterology, 2021. Pooled analysis of 36 randomised trials, 9,312 adults; adverse events relative risk 1.00; no conflicts declared. PubMed 33234881.
3. Esmaeilinezhad Z, et al. Probiotics for the prevention of Clostridioides difficile-associated diarrhea in adults and children. Cochrane Database of Systematic Reviews, 2025. Cochrane review, 47 randomised trials, 15,260 people; adverse events from 37 trials, 11,911 people; no funding for the update. PubMed 40931979.
4. Guo Q, et al. Probiotics for the prevention of pediatric antibiotic-associated diarrhea. Cochrane Database of Systematic Reviews, 2019. Cochrane review, 33 randomised trials, 6,352 children; adverse events from 24 trials, 4,415 children. PubMed 31039287.
5. Ouwehand AC. A review of dose-responses of probiotics in human studies. Beneficial Microbes, 2017. Review; author employed by a culture supplier. PubMed 28008787.
6. NHS. Probiotics. Page last reviewed 24 November 2022 (review overdue). nhs.uk/conditions/probiotics.
7. Doron S, Snydman DR. Risk and safety of probiotics. Clinical Infectious Diseases, 2015. Review. PubMed 25922398.

General information, not medical advice. Live cultures are a food supplement; follow the label dose, and talk to a doctor first if you have an existing health condition or a weakened immune system.