Probiotics, Mood and Anxiety: Gut-Brain Axis Claims and Trial Evidence

If you are struggling, start here

If you are thinking about harming yourself or you are in immediate danger, call or text 988 (Suicide & Crisis Lifeline, US) or call 911. Ongoing low mood, worry that gets in the way of daily life, or changes in sleep and appetite deserve an assessment by a clinician; see anxiety disorders and how stress, anxiety, burnout and depression differ. Do not stop or change a prescribed medicine because of anything you read here; talk to the prescriber.

The short answer

The "gut-brain axis" is the proposed link between the gut and the brain, and "psychobiotics" is the term for probiotics proposed to benefit mental health through it. [1] Pooled trials report small to moderate average improvements in depression and anxiety scores [2][3], but the trials are small, vary in strain and design, and are very mixed in quality. That is promising but limited evidence, not an established treatment. For the research background, see the gut-brain axis and microbiome research and mental health.

Evidence labels: promising but limited, mixed, insufficient evidence, marketing claim. Study amounts are what researchers tested, not advice.

What pooled trials found

Label: promising but limited. Biomarker or score changes on a questionnaire are not the same as recovery, and none of these reviews can tell you which product to use. The 2019 and 2025 authors both called for more and better trials. [2][3]

One trial in detail

A pilot trial in London enrolled adults aged 18 to 55 with major depressive disorder who were taking an antidepressant but had an incomplete response. [5] It was a single-center, double-blind, placebo-controlled study: 24 people received a multistrain probiotic (8 billion CFU a day) and 25 received placebo for 8 weeks, added to their usual medicine. [5] There were no serious adverse reactions, and the authors judged the results promising enough to justify a definitive trial. [5] A 49-person pilot cannot show that a probiotic works, and the result applies to that multistrain product only. See why trials disagree.

Why the results are hard to read

• Strains differ. The 2025 BMC Psychiatry review found the effect varied by probiotic type. [3]
• People differ. The 2025 BMC Psychiatry review included people with diagnosed disorders as well as people with symptoms alongside chronic disease or in the general population [3], and the 2019 review found larger effects in clinical samples but few such trials. [2]
• Indirect comparisons. A 2025 network meta-analysis compared probiotics with antidepressants by combining separate placebo-controlled trials, and it noted a lack of head-to-head trials; its certainty of evidence was moderate to very low. [6] Do not read it as showing that a probiotic can replace an antidepressant.
• Marketing. Label claims such as "mood support" are not proof of benefit. See probiotic myths.