The Psychobiotics in Depression and Anxiety: Efficacy, Mechanisms, and the Underestimated Risk of Antibiotic Resistance

Background. Depression and anxiety are highly prevalent, and up to one-third of depressed patients fail to achieve remission despite standard pharmacotherapy. This gap has prompted interest in the gut microbiome, via the gut - brain axis, as an adjunctive target. Psychobiotics - probiotics, prebiotics, synbiotics, and postbiotics with documented mental health effects - are promising, though their microbiological safety remains underexplored. Aim. To synthesize evidence on psychobiotic efficacy in depression and anxiety, outline gut-brain mechanisms, and highlight safety concerns regarding antimicrobial resistance transfer from bacterial formulations. Material and methods. This narrative review was based on a literature search of PubMed and Google Scholar, identifying clinical trials, meta-analyses, and studies on gut-brain communication, microbiota composition in depression/anxiety, psychobiotic efficacy, and antibiotic resistance in probiotic strains. Results. Four gut-brain pathways were identified: vagal, HPA-axis, immune, and tryptophan/serotonin routes. Depression and anxiety are linked to dysbiosis with reduced butyrate-producing and increased pro-inflammatory taxa; causality is supported by fecal transplantation studies. Probiotics show the strongest evidence for antidepressant and anxiolytic effects, especially as pharmacotherapy adjuncts. Evidence for other forms remains limited. Many probiotic strains carry mobile antibiotic resistance genes, and their use during antibiotic therapy has been linked to expansion of the gut resistome, raising safety concerns. Conclusions. Probiotics offer the most robust evidence for adjunctive treatment; other forms need further research. Strain selection should weigh both efficacy and resistance safety.