Blood serotonin rose in both groups in a probiotic trial
In Australian adults with depressive symptoms below the diagnostic threshold, probiotics and placebo showed overlapping blood-marker changes. The abstract does not establish a mental-health benefit.
Based on the published abstract. The full paper may contain additional methods, results and limitations.
The 30-second takeaway
In adults with depressive symptoms below the diagnostic threshold, the probiotic and placebo groups both showed an early rise in blood serotonin. A later statistically significant rise appeared only with placebo, while GABA, another signaling chemical, showed no significant change. These blood measurements do not establish improved symptoms or prevention of depression.
This secondary analysis reports blood-marker results without units for the changes or mental-health outcome estimates. The abstract does not present evidence establishing safety or prevention of severe depression.
Within-group changes need care
Serotonin increased significantly in both groups at 6 weeks, but only with placebo at 12 weeks. A significant result in one group and an unclear result in another do not establish a difference between groups.
Blood markers and clinical claims
Measurements came from blood, and the abstract reports no corresponding symptom-result estimates. Its prevention claim therefore goes beyond the clinical results presented: a pattern in signaling chemicals does not demonstrate prevention of a depressive disorder.
The original publication
Exploring neurotransmitter regulation following probiotic supplementation in adults with subthreshold depression: A secondary analysis of a randomized controlled trial.
Dacaya P, Sarapis K, Hall R et al.
Nutrition · 2025
- PubMed ID
- 40729791
- Record checked
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