TABLE 2.
Summary of key study characteristics and outcomes.
| References | Study population | Study design | Sample size | Mean age (%F) | Country | Intervention type | Duration | Probiotic | Outcome measures | Conclusion |
| Arifdjanova et al., 2021 | Mild-moderate MDD (ICD-10), 18–45yo | Placebo, double-blind RCT | n = 149 | 32.9 (62.2%) | Russia | Cipralex (SSRI) + Placebo or Probiotic | 6 weeks | Bac-Set Forte* 3 capsules/day (1010 CFU) | HAM-D for depression severity, ELISA for cortisol and cytokines, HPLC for blood plasma | Found decreased levels of cortisol, dopamine, IL-6, TNF-a and nitric oxide, and a bigger reduction in depressive symptoms in the adjuvant PB group compared to standard therapy. |
| Rudzki et al., 2019 | Moderate MDD (DSM-IV-R) | Placebo, double-blind RCT | n = 60 | 39 (71%) | Poland | Antidepressant (various SSRIs) + Probiotic or Placebo | 8 weeks | 2 capsules/day (10 × 109 CFU of Lactobacillus Plantarum 299v each) | Symptom Severity: HAM-D 17, SCL-90, PSS-10, cognitive function, biochemical parameters also assessed | PB correlated with increased cognitive performance and decreased kynurenine concentration in MDD patients, no significant effect on symptom severity. |
| Ghorbani et al., 2018 | Moderate MDD (DSM-V), 18–55yo | Placebo, double-blind RCT | n = 40 | 34.8 (70%) | Iran | Fluoxetine (SSRI, 20 mg/day - 4W) then Fluoxetine + synbiotic capsule or Placebo (6W) | 6 weeks | 1 capsule/day (MS probiotic**, 500 mg + prebiotic, 100 mg) | HAM-D primary outcome | Found a greater reduction in HAM-D scores in synbiotic treated patients compared to the placebo group. |
| Kazemi et al., 2019 | Mild-moderate MDD (ICD-10) on medication, 18–50yo | Three-arm placebo, double-blind RCT | n = 81 | 36.5 (70.9%) | Iran | Antidepressant (sertraline, fluoxetine, citalopram, amitriptyline) + Probiotic or Prebiotic or Placebo | 8 weeks | 1 sachet/day - probiotic (≥10 × 109 CFU Lactobacillus helveticus and Bifidobacterium longum), or prebiotic (galactooligosaccharide) | BDI primary outcome, HPLC for serum tryptophan and branched chain amino acids, ELISA for kynurenine | PB resulted in a decrease in BDI score and increased tryptophan/isoleucine ratio compared to placebo and prebiotic. No significant results for prebiotic and placebo groups |
| Miyaoka et al., 2018 | Treatment Resistant MDD (DSM-IV) | Prospective open label randomized | n = 40 | 43.5, (60%) | Japan | Antidepressant (fluvoxamine, paroxetine, escitalopram, duloxetine, and sertraline) with or without (control) Probiotic | 8 weeks | 60 mg/day (Clostridium butyricum MIYAIRI (CBM588)–10 CFU/gram) | HAM-D, BDI and the Beck Anxiety Inventory | PB correlated to significant improvement in depression regardless of antidepressant type; well tolerated. |
| Eskandarzadeh et al., 2021 | Drug-free patients with GAD (DSM-V), 18–65yo | Placebo, double-blind RCT | n = 48 | 33.9 (81.2%) | Iran | Sertraline (SSRI, 25 mg/day) + Placebo or Probiotic | 8 weeks | 1 capsule/day (18*109 CFU Bifidobacterium longum, Bifidobacterium bifidum, Bifidobacterium lactis and Lactobacillus acidophilus) | HAM-A scale for anxiety, Beck Anxiety Inventory, State-Trait Anxiety Inventory | Found Sertraline + PB group to have improved clinical outcome measures as opposed to Sertraline + placebo. Significance varied depending on scale used. |
| Dickerson et al., 2014 | Mild-moderate SZ (DSM-IV, PANSS), 18–65yo | Placebo, double-blind RCT | n = 65 | 46.2 (35.4%) | U.S. | Antipsychotic (various) + Placebo or Probiotic | 14 weeks | 1 Capsule/day (109 CFU combined Lactobacillus rhamnosus strain and Bifidobacterium animalis subsp. lactis strain Bb12) | PANSS to measure psychiatric symptoms + difficulty of bowel movement scale | No significant difference in psychiatric scores, PB well tolerated, PB group had less bowel problems associated w/treatment. |
| Yang et al., 2021 | First-episode SZ or SZA (DSM-V), 18–55yo | Open-label, RCT | n = 67 | 43.2 (67.7%) | China | Olanzapine with or without (control) Bifidobacterium group | 12 weeks | 3 capsules/day (live combined Bifidobacterium, Lactobacillus, and Enterococcus capsules; 1 × 109 CFU each) | Body weight, BMI, appetite, latency to increased appetite, and baseline weight increase of more than 7%, PANSS to measure psychiatric symptoms |
No significant differences in PANSS scores. In the first 4 weeks there was reduced weight change and BMI for PB group, but this difference disappeared after 4 weeks. There were no overall differences in appetite. |
*Contents of Bac-Set Forte: Streptococcus thermophilus; Bifidobacterium ssp; Lactobacillus ssp. among others. **Contents of MS probiotic: L. casei = 3 × 108, L. acidophilus = 2 × 108, L. bulgaricus = 2 × 109, L. rhamnosus = 3 × 108, B. breve = 2 × 108, B. longum = 1 × 109, S. thermophilus = 3 × 108.