In a recent open-label pilot study[1], a group of researchers from the Center of Neuroscience Studies and department of Psychiatry at Queen's university conducted an intervention on a group for 10 patients diagnosed with Major Depressive Disorder (MDD). The treatment lasted 8 weeks and consisted of a probiotic supplement containing Lactobacillus helveticus R0052 and Bifidobacterium longum at a dose of 3 × 10⁹ CFU once per day. Data was collected at baseline, week 4 and week 8. Results were measured with several clinical depression scales, and self-report questionnaires. At 4 weeks there were significant improvements in affective clinical symptoms, and these effects were sustained by week 8. There were also significant improvements in sleep quality by week 8, and no adverse effects from supplementation. While the sample size is small, these findings suggest groundwork for larger placebo-controlled clinical trials on the use probiotics for symptoms of depression. What is unique is that this study investigated probiotics as a standard, monotherapy for individuals not taking antidepressants.