Do probiotics help with depression? What the research does and doesn't show

The evidence doesn't support probiotics as a treatment for depression. Meta-analyses find average score improvements over placebo, about 2 points on one scale in a pool of 776 people, but trials differ widely and none identifies a strain, dose or duration that works. A score change in a trial is not a treatment result.

What the evidence doesn't support

It doesn't support a probiotic as a treatment for depression or low mood, and it doesn't support the idea that any particular strain or amount works. The trials differ in strain, dose, duration and who was enrolled, and the reviews that pool them report high variation between trials. A review of 249 trials across probiotic uses found that effects are strain-specific and purpose-specific and that many products have no trial of their own, so a result for one named strain doesn't transfer to a product that lists only species.

What the trials found

A 2023 meta-analysis pooled randomized trials in 776 people with depressive symptoms (397 probiotic, 379 control). Beck Depression Inventory scores were lower with probiotics (mean difference -1.98, 95% CI -3.14 to -0.82), about 2 points. On a second depression scale in the same analysis, DASS, the difference was not significant (MD 0.90, 95% CI -1.17 to 2.98). Pooled markers of inflammation were mixed: IL-6 was lower, TNF-alpha did not differ.

A 2019 meta-analysis of 34 controlled trials found a small effect of probiotics on depression scores overall (d = -0.24). The effect was larger in clinical or medical samples (d = -0.45), and larger again in a preliminary analysis restricted to psychiatric samples (d = -0.73). The authors noted that the pooled effect was held down by how few trials had enrolled people with a clinical diagnosis. Prebiotics alone did not differ from placebo.

A 2025 meta-analysis limited to people with a clinical diagnosis pooled 23 randomized trials (1,401 patients) and reported a large reduction in depression symptoms with probiotics versus placebo (SMD -0.96, 95% CI -1.31 to -0.61, from 18 trials), with high heterogeneity across studies. The authors said study duration and probiotic formulation contributed to the variation.

In healthy volunteers, a 2017 meta-analysis of 7 placebo-controlled studies found a small improvement in a combined score of everyday depression, anxiety and perceived stress (SMD 0.34, 95% CI 0.07 to 0.61).

Review	People	Result versus placebo
2023, 776 adults	Depressive symptoms	BDI about 2 points lower; DASS no significant difference
2019, 34 trials	Mixed samples	Small effect; larger in clinical samples
2025, 23 trials	Clinically diagnosed	Large reduction in symptom scores, high heterogeneity
2017, 7 studies	Healthy volunteers	Small improvement in combined symptom score

The reviews measure symptom scores. They don't show that a probiotic treats depression, and they don't say which strain to take, how much, or for how long. Larger, strain-specific trials would settle more than another pooled analysis.

Probiotic effects are strain-specific, so a result for one named strain is not a result for "probiotics" in general, and a product that lists species without strain codes can't borrow it. See what the research shows across probiotics and how to choose a probiotic.

Questions people ask

Do probiotics help with depression?

On average, trial groups taking probiotics had depression-scale scores somewhat below those of placebo groups, by an amount that varies from about 2 points on one scale to large effects in diagnosed groups. That is a result about scores in specific trials, not evidence that a probiotic treats depression.

Which probiotic is best for depression?

The reviews above don't rank strains, and a product that lists species without strain codes can't be matched to any trial. See how to choose a probiotic.

What about anxiety?

That literature is separate and less consistent: see what the research shows for anxiety.

When to talk to a doctor

Persistent low mood, loss of interest, changes in sleep or appetite, or any thought of self-harm is a reason to talk to a doctor or mental-health professional now. A probiotic is not a treatment for depression, and nothing above supports using one in place of care. If you are in crisis, contact local emergency services or a crisis line. If you take prescription medication, are pregnant or nursing, or have a weakened immune system, ask a doctor before adding any supplement (see who should not take probiotics).