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

The evidence does not support probiotics as a way to relieve stress in a way you would notice. In healthy adults, pooled trials found slightly lower self-reported stress scores, and one review found no change in cortisol while another found a small drop. Effects were modest, and strains, doses and measures varied.

What the evidence doesn't support

• No anxiety, depression or stress-disorder treatment was shown: the healthy-volunteer reviews measured subclinical symptom scores.
• A reliable change in cortisol. One review of seven trials found no significant change; another of 12 found a modest one.
• A change in inflammation. In 12 trials of healthy working adults, there was no significant effect on C-reactive protein.
• One strain or dose. The reviewers attributed heterogeneity to varied strains, doses and durations.
• The same from prebiotics. In 24 healthy adults, 10 g a day of fructooligosaccharide plus galactooligosaccharide for four weeks changed gut bacteria but not stress or inflammation markers or mood.

What the trials found

Healthy volunteers

A 2020 systematic review and meta-analysis of seven randomized trials (1,146 healthy volunteers) found probiotics generally reduced subjective stress and may have improved stress-related subthreshold anxiety and depression, but no significant effect appeared in subgroup analyses and cortisol did not change significantly. A 2017 meta-analysis of seven placebo-controlled trials in healthy volunteers found a statistically significant improvement in psychological symptoms (standardized mean difference 0.34, 95% CI 0.07 to 0.61) versus placebo.

Healthy working adults

A 2026 meta-analysis of 12 trials in 3,350 healthy employed adults found a modest positive effect on depression, anxiety and stress symptoms (SMD -0.21, 95% CI -0.34 to -0.09) and cortisol (SMD -0.26, 95% CI -0.45 to -0.08), no significant effect on CRP, and too little evidence on sleep. Strains and doses varied.

Mood and anxiety in broader groups

A 2025 analysis of 72 trials of probiotics, prebiotics and synbiotics versus placebo found depression (SMD -0.53) and anxiety (SMD -0.44) scores improved, with high heterogeneity and limited methodological quality; the trials included people with anxiety and depression disorders, chronic disease and healthy people with symptoms.

Questions people ask

Do probiotics help with stress?

Self-reported stress scores were slightly lower in healthy volunteers across several small trials. The measures are subjective, effect sizes modest and no strain or dose is established. Cortisol results conflict.

Do probiotics help anxiety or mood?

The 72-trial analysis found small-to-moderate score improvements with large variability; it is not a treatment recommendation. Persistent anxiety or low mood is for a doctor.

See also probiotics and sleep, probiotics and inflammation and probiotics benefits.

When to talk to a doctor

A probiotic is not a treatment for stress, anxiety or depression. Persistent low mood, constant worry, panic, thoughts of self-harm or stress that affects work or relationships should be assessed by a doctor or mental health professional; in a crisis, contact local emergency services. Ask a doctor or pharmacist before starting a probiotic if you have a weakened immune system or take prescription medicine.