Previous research from a meta-analysis of seven randomized, controlled trials indicated that the use of probiotics appears to be effective in diminishing depressive symptoms when administered adjunctively to antidepressants; however, more research was warranted. In a recent study, researchers have discovered evidence that supplementing the diet with a probiotic blend containing 14 strains of bacteria can help individuals who are being treated for MDD with antidepressants.

In a recent publication in JAMA Psychiatry, researchers from Kings College London conducted a single-center, double-blind, placebo-controlled, pilot randomized clinical trial to provide acceptability and tolerability data and estimates of intervention effect size for probiotics as an adjunctive treatment for patients with MDD.

The trial involved adults aged 18 to 55 years with MDD taking antidepressant medication but having an incomplete response. A random sample was recruited from primary and secondary care services and general advertising in London, United Kingdom. Data were collected between September 2019 and May 2022 and analyzed between July and September 2022.

The researchers indicated that for this study, multistrain probiotics (8 billion colony-forming units [CFUs] per day) or a placebo daily for 8 weeks added to ongoing antidepressant medication were used.

The authors wrote, “The pilot outcomes of the trial were retention, acceptability, tolerability, and estimates of putative treatment effect on clinical symptoms (depression: Hamilton Depression Rating Scale [HAMD-17] and Inventory of Depressive Symptomatology [IDS] scores; anxiety: Hamilton Anxiety Rating Scale [HAMA] and General Anxiety Disorder [GAD-7] scores) to be used as indicators for a definitive trial.”

The results revealed that of 50 included participants, 49 adults with diagnosed MDD and with an incomplete response to prescription antidepressants were provided with an extensively available, proprietary 14-strain blend probiotic supplement or an identical placebo. A total of 24 were randomized to probiotics and 25 to placebo. Participants were randomized 1:1 to four capsules daily of probiotic (2x109 CFUs per capsule) or matching placebo.

The participants were comprised of the following: 39 (80%) were female and the mean (SD) age was 31.7 (9.8) years. The authors indicated that over the course of 8 weeks, both groups demonstrated improvement in their symptoms, but more significant improvements were observed in the group with daily probiotic intake for 8 weeks, resulting in more significant improvements in depressive and anxiety symptoms compared with placebo.

The authors concluded, “The preliminary findings from this pilot study suggest that 8-week adjunctive treatment with a multi-strain probiotic is acceptable and tolerable for adults with MDD. The estimated effect sizes on key clinical outcomes are promising and encourage further investigation in a definitive efficacy trial.”

The authors stated, “The pilot study is one of the first trials in a Western population to show both good tolerability of probiotics and positive effects on mental health in adults with depression currently taking antidepressants.”

According to the researchers leading the study, the results provided a robust foundation to further explore the benefits of this probiotic food supplement for supporting mood and mental health in a larger trial.

Professor James Stone, the study’s senior investigator who began the work at the Institute of Psychiatry, Psychology & Neuroscience at King’s College London and is now at Brighton and Sussex Medical School, stated, “Non- or partial response to antidepressants is a huge problem, and this study is an important first step in exploring the therapeutic potential of probiotics as a treatment for depression. We found that probiotics were an acceptable and tolerable supplement in people already taking antidepressant medications. This now paves the way for studies looking at whether we see these beneficial effects of probiotics on depression and anxiety in larger populations of patients.”

Lead author Dr. Viktoriya Nikolova stated, “The gut-brain axis is a truly fascinating and rapidly evolving area of microbiome research. The findings of this pilot study are an important step forward in our understanding of the role of probiotics in mood and mental health.”

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