Date of Award


Degree Type

Selective Evidence-Based Medicine Review

Degree Name

Master of Science in Health Sciences - Physician Assistant


Physician Assistant Studies


Objective: The objective of this selective EBM review is to determine, “Do probiotics decrease depressive symptoms in patients with low mood?”

Study Design: A systematic review of three double blind, randomized control trials (RCTs) published between 2016 and 2019.

Data Sources: All three RCTs were found using PubMed and published in English in peer-reviewed journals. The articles were chosen based on their attention to patient-oriented evidence that matters (POEMS) and their relevance to the clinical question.

Outcome Measured: All three articles utilized either the Beck Depression Index (BDI) and/or the Depression Anxiety Stress Scale (DASS) to measure the severity of depressive symptoms. The higher the score, the more severe the level of depression. The between group difference, F-score, or mean change from baseline were calculated from scores recorded before and after intervention.

Results: The decrease in depressive symptoms of the placebo group compared the probiotic group were found significant in one out of the three RCTs reviewed. Romjin et al. observed a between group difference of -0.03(-4.1, 4.1) in DASS-42 scores (p ≥0.05). Chahwan et al. observed an F score of 0.00 (p ≥0.05) for BDI-II scores, and an F score of 0.20 (p ≥0.05) for DASS-21 scores. Akkasheh et al. found the change from baseline of BDI-I scores between the placebo and probiotic group significant (p = 0.001), however this effect may have been influenced by confounding variables.

Conclusions: Results from these three studies suggest the use of probiotics in decreasing depressive symptoms in patients with low mood is not effective. More research is needed before probiotics can be considered standard monotherapy, however its use as adjunctive treatment is promising. Future studies should standardize the probiotics used and specify which severity of depression or which symptom of depression probiotics are most effective at treating