It is known that a significant percentage of individuals with major depressive disorder (MDD) do not respond to standard treatments, and the microbiota-gut-brain axis has emerged as a promising target for novel therapies. A recent pilot study investigated the use of adjunctive probiotics as a potential treatment for MDD. The researchers conducted an 8-week randomized double-blind placebo-controlled trial involving 50 outpatients diagnosed with MDD taking antidepressant medication but having an incomplete response (92% taking selective serotonin reuptake inhibitor [SSRI]). The participants were randomly assigned to receive either a multistrain probiotic (8 billion colony-forming units per day) or a placebo, and their depressive symptoms were measured using the Hamilton Depression Rating Scale (HAMD-17) and the Inventory of Depressive Symptomatology (IDS) Self Report. Other outcomes, such as anxiety levels, clinical status, adherence, and tolerability were also assessed. The results showed that the probiotic group exhibited greater improvement in depressive symptoms compared to the placebo group. The effect sizes were moderate and comparable to those reported in earlier meta-analyses. The probiotic treatment also showed potential in reducing anxiety symptoms. The intervention was well tolerated, with high adherence and no serious adverse reactions. However, there are limitations to consider. The study does not determine whether the observed effects are specific to the interaction with SSRIs or applicable to other treatments. Additionally, adherence was assessed through capsule count, which may lead to overreporting. In conclusion, this pilot study suggests that an 8-week adjunctive treatment with a multistrain probiotic is acceptable and tolerable for individuals with MDD. The results indicate promising effect sizes on key clinical outcomes and support the need for further investigation in a definitive efficacy trial.

Reference:

Nikolova VL et al. JAMA Psychiatry 2023;e231817. Abstract