Nelson Vergel
Founder, ExcelMale.com
The study was published in JAMA Psychiatry recently. It was a single-center, double-blind, placebo-controlled pilot randomized clinical trial, and it aimed to evaluate the acceptability, tolerability, and potential efficacy of probiotics as an adjunctive treatment for patients with major depressive disorder (MDD). The participants were adults aged 18 to 55 years with MDD who were taking antidepressant medication but experiencing an incomplete response to treatment. They were given a multistrain probiotic (8 billion colony-forming units per day) or a placebo daily for 8 weeks in addition to their ongoing antidepressant medication.
The trial reported no serious adverse reactions, high adherence to the treatment protocol, and low attrition. Furthermore, the study found that the probiotic group showed greater improvements in depressive symptoms according to the Hamilton Depression Rating Scale (HAMD-17) and the Inventory of Depressive Symptomatology (IDS) scores, as well as greater improvements in anxiety symptoms according to the Hamilton Anxiety Rating Scale (HAMA) scores, compared with the placebo group.
However, the study authors stressed that these results are preliminary, and a definitive efficacy trial is needed to further investigate the potential of probiotics as an add-on treatment for people with MDD1.
jamanetwork.com
I checked and found out this is the product they used:
The trial reported no serious adverse reactions, high adherence to the treatment protocol, and low attrition. Furthermore, the study found that the probiotic group showed greater improvements in depressive symptoms according to the Hamilton Depression Rating Scale (HAMD-17) and the Inventory of Depressive Symptomatology (IDS) scores, as well as greater improvements in anxiety symptoms according to the Hamilton Anxiety Rating Scale (HAMA) scores, compared with the placebo group.
However, the study authors stressed that these results are preliminary, and a definitive efficacy trial is needed to further investigate the potential of probiotics as an add-on treatment for people with MDD1.

Acceptability, Tolerability, and Treatment Effects of Probiotics as Adjunctive Treatment in Depression
This pilot randomized clinical trial evaluates acceptability and tolerability data and estimates of intervention effect size for probiotics as adjunctive treatment for patients with major depressive disorder.

I checked and found out this is the product they used: