Can Probiotics Make You Anxious? What the Trials Record

No. No trial or pooled analysis has found that live cultures raise anxiety. Across 34 controlled trials pooled in 2019, anxiety scores moved slightly the other way (d = -0.10)¹; across 12 anxiety trials in 1,551 people pooled in 2018 they did not differ from placebo²; and the adverse events recorded across two pooled analyses of more than 20,000 trial participants are wind, cramping and looser stools, not anxiety.^{3, 4} This page is one spoke of the Wellgard probiotics guide.

Evidence at a glance

• Trials: 34 controlled trials of mood and anxiety pooled in 2019; 12 anxiety trials, 1,551 people, pooled in 2018; 16 trials, 1,125 people, pooled in 2021; adverse events from 36 trials in 9,312 adults and 37 trials in 11,911 people.
• Largest pooled anxiety analysis: 12 randomised trials, 1,551 people, all rated at low or moderate risk of bias (2018).
• Strongest measured outcome: State-Trait Anxiety Inventory scores 6.88 points lower than placebo (95% confidence interval -12.35 to -1.41; low certainty) in the 2021 pooling of people with depressive or anxiety symptoms.
• Not yet tested: no trial has been designed to ask whether live cultures cause anxiety; the absence of a signal is an adverse-event count from trials run for other reasons.

Sources checked on 16 October 2026.

Can probiotics make you anxious?

Not according to anything that has been measured. Two kinds of evidence answer the question. The first is the anxiety trials themselves: when researchers gave live cultures and scored anxiety, the scores either did not change or fell a little. The 2018 pooling of 12 randomised trials found "no significant difference between probiotics and placebo in alleviating anxiety symptoms".² The 2019 pooling of 34 controlled trials found a small reduction (d = -0.10, P = 0.03).¹

The second is the safety count from trials run for other reasons. Across 36 randomised trials in 9,312 adults taking antibiotics, adverse events were no more common on live cultures than on placebo (relative risk 1.00, 0.87 to 1.14).³ In a 2025 Cochrane review, 37 trials in 11,911 people recorded adverse events in 10.9% of those on live cultures and 12.2% of controls; the most common in both groups were "abdominal cramping, nausea, fever, soft stools, flatulence, and taste disturbance".⁴ Anxiety is not on the list. The 2021 pooling of mood trials found no statistically significant difference in adverse events either.⁵ One caveat sits beside those counts: a 2015 safety review notes that trials report safety outcomes "inconsistently", so absence from the list is a count, not a guarantee.⁶

Is anxiousness a side effect of taking a probiotic?

It is not a recorded one. The recorded early effects are gut effects: wind, bloating, cramping and a looser stool in the first days, at rates no higher than placebo.^{3, 4} The overlap is physical. The NHS lists among the bodily symptoms of anxiety "indigestion, stomach cramps, bloating and feeling sick (nausea)" and "constipation or diarrhoea".⁷ A bloated, gurgling first week on a new capsule can feel like the stomach side of anxiety, and anxiety can produce the same bloating with no capsule involved. The practical test is time. If gut symptoms have not settled within a week or two, stop the capsule and see whether they go; if the anxious feeling stays once the stomach has settled, it has another cause and deserves attention in its own right. The full side-effect record is on the side effects of too much probiotics.

Can probiotics cause brain fog or restlessness?

One case series says possibly, and it is disputed. In 2018, US clinicians described 30 people with gas, bloating and "brain fogginess", all of whom were taking live cultures; 68% had bacterial overgrowth of the small intestine against 28% of eight similar patients without brain fog, and 77% had D-lactic acidosis against 25%. After stopping the cultures and a course of antibiotics, brain fog resolved and gut symptoms improved in 23 of 30.⁸ Three researchers with declared industry interests replied that the cultures had not been shown to be the cause.⁹ It is a single-centre report about people with overgrowth, not a trial, and neither restlessness nor anxiety was among its outcomes. Tiredness has its own page: can probiotics make you tired.

Is there a link between gut health and anxiety?

In one direction, certainly: the NHS describes anxiety producing stomach cramps, bloating, nausea, constipation or diarrhoea.⁷ The other direction, whether changing the gut's bacteria changes anxiety, is what the trials in the next section test, and their answer is small effects in some groups and none in others. The gut-brain axis is a real field of research. It is not yet a reason to expect a capsule to change how anxious you feel.

Can probiotics help with anxiety?

A little, in some people, and the clearest results are in people with a diagnosis. The 2019 pooling of 34 trials found small effects on depression (d = -0.24) and anxiety (d = -0.10); prebiotics showed no significant effect on either.¹ The 2018 pooling of 12 anxiety trials found no difference from placebo.² A 2020 pooling of 10 trials in 685 people found depression scores improved only in people with a depression diagnosis, no change in anxiety scores in anyone, and no effect in healthy people under stress.¹⁰ In 16 trials of people with depressive or anxiety symptoms (1,125 people), State-Trait Anxiety Inventory scores were 6.88 points lower than placebo (low certainty), while the Beck Anxiety Inventory and the DASS anxiety scale showed no difference.⁵ Restricted to clinically diagnosed samples, a 2025 pooling of nine anxiety trials found a moderate reduction (standardised mean difference -0.59, -0.98 to -0.19), with high heterogeneity and the culture usually taken alongside treatment.¹¹

Read together: the healthier and less anxious the people in the trial, the smaller the effect; in diagnosed patients taking them with treatment, the effect is real but inconsistent between scales and trials, and no trial reports remission. The mood side of the evidence, including which species were tested, is on what psychobiotics do.

When anxiety needs more than a supplement

The NHS is specific. See a GP if "you're struggling to cope with anxiety, fear or panic" or "things you're trying yourself are not helping".⁷ If you are 18 or over (16 or over in some areas) you can refer yourself to an NHS talking therapies service without speaking to a GP; the service covers "anxiety, including social anxiety and panic disorder" and "coping with a long-term health condition, such as irritable bowel syndrome (IBS)".¹² Samaritans are on 116 123 "at any time, day or night".⁷ A capsule does not undercut any of that, and it does not replace any of it.

What we don't know

• No trial has been designed to test whether live cultures cause anxiety; the no-signal finding is an adverse-event count from trials of other outcomes.
• The anxiety trials score questionnaires over a few weeks; none reports remission, and none follows people after stopping.
• No pooled analysis separates species for anxiety; the species lists come from depression trials.
• The brain-fog series cannot separate the cultures from the bacterial overgrowth as the cause.

Frequently asked questions

Do probiotics cause anxiety?

No pooled analysis or trial reports it. Anxiety scores were unchanged or slightly lower in the trials that measured them, and anxiety is not among the adverse events recorded in two pooled analyses of more than 20,000 trial participants.^{1, 2, 3, 4}

Should I stop probiotics if I feel anxious?

Stopping for a week or two is a fair test. If the anxiety continues once any stomach symptoms have settled, speak to a GP or refer yourself to NHS talking therapies.^{7, 12}

Are probiotics good for panic attacks?

No trial has tested live cultures for panic attacks. The NHS says a panic attack "usually lasts 5 to 20 minutes" and that panic attacks "are not dangerous and should not harm you"; its page sets out the self-help steps and when to see a GP.⁷

Which probiotics are best for anxiety?

No pooled analysis ranks a species for anxiety. In the depression trials the species were Lactobacillus acidophilus, paracasei, casei, plantarum and salivarius and Bifidobacterium bifidum, lactis, breve and longum, with a 2.69-point drop on the Beck Depression Inventory across seven trials and no significant change on three other scales.¹³

Sources

1. Liu RT, Walsh RFL, Sheehan AE. Prebiotics and probiotics for depression and anxiety: A systematic review and meta-analysis of controlled clinical trials. Neuroscience and Biobehavioral Reviews, 2019. Pooled analysis of 34 controlled trials. PubMed 31004628.
2. Liu B, et al. Efficacy of probiotics on anxiety-A meta-analysis of randomized controlled trials. Depression and Anxiety, 2018. Pooled analysis of 12 randomised trials, 1,551 people. PubMed 29995348.
3. 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. PubMed 33234881.
4. 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. PubMed 40931979.
5. El Dib R, et al. Probiotics for the treatment of depression and anxiety: A systematic review and meta-analysis of randomized controlled trials. Clinical Nutrition ESPEN, 2021. Pooled analysis of 16 randomised trials, 1,125 people. PubMed 34620373.
6. Doron S, Snydman DR. Risk and safety of probiotics. Clinical Infectious Diseases, 2015. Review. PubMed 25922398.
7. NHS. Anxiety, fear and panic. nhs.uk. Page last reviewed 13 July 2026.
8. Rao SSC, et al. Brain fogginess, gas and bloating: a link between SIBO, probiotics and metabolic acidosis. Clinical and Translational Gastroenterology, 2018. Observational case series, 30 patients with brain fogginess and 8 without; no external funding. PubMed 29915215.
9. Quigley EMM, Pot B, Sanders ME. 'Brain Fogginess' and D-Lactic Acidosis: Probiotics Are Not the Cause. Clinical and Translational Gastroenterology, 2018. Letter; authors declare industry interests. PubMed 30250026.
10. Chao L, et al. Effects of Probiotics on Depressive or Anxiety Variables in Healthy Participants Under Stress Conditions or With a Depressive or Anxiety Diagnosis: A Meta-Analysis of Randomized Controlled Trials. Frontiers in Neurology, 2020. Pooled analysis of 10 randomised trials, 685 people. PubMed 32528399.
11. Asad A, et al. Effects of Prebiotics and Probiotics on Symptoms of Depression and Anxiety in Clinically Diagnosed Samples: Systematic Review and Meta-analysis of Randomized Controlled Trials. Nutrition Reviews, 2025. Pooled analysis of 20 randomised trials, 1,401 patients; anxiety from 9 trials. PubMed 39731509.
12. NHS. NHS talking therapies for anxiety and depression. nhs.uk. Page last reviewed 5 November 2025.
13. Rahmannia M, et al. Strain-specific effects of probiotics on depression and anxiety: a meta-analysis. Gut Pathogens, 2024. Pooled analysis of 12 randomised trials, 707 people. PubMed 39245752.

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