Canadian Network Backs Probiotics for MDD as 3rd-Line Adjunctive Treatment

1 articles · Updated · Psychology Today · Aug 20

Adults with major depressive disorder may now be considered for probiotics as a cautious third-line add-on treatment, the Canadian Network for Mood and Anxiety Treatments said after reviewing microbiome interventions.
Few adverse events and generally good tolerability helped support that recommendation, though the group stopped short of endorsing probiotics as a replacement for standard depression therapy.
Meta-analyses behind the shift have shown mixed but positive efficacy signals: a 2026 review found a moderate depression benefit with a standard mean difference of -0.5, while anxiety effects were smaller at -0.19.
Earlier pooled data were stronger but less consistent, including a 2024 analysis of 969 depression patients that reported an SMD of -0.96, with wide variation in strains, doses and study methods clouding interpretation.
The recommendation adds cautious clinical weight to a field still trying to standardize evidence on the gut-brain axis, even as imaging studies and psychiatrist experience suggest psychobiotics can complement conventional care.