The Impact of Psychobiotic Therapy on Anxiety and Depressive Symptoms in Patients with Post-COVID Syndrome—A Randomized, Double-Blind, Placebo-Controlled Trial

Background: Recovering from COVID-19 does not always lead to complete recovery, and many patients report symptoms of anxiety and depression. One potential mechanism behind these disorders is dysbiosis. The aim of this study was to evaluate the impact of psychobiotic therapy on the effectiveness of treating anxiety and depressive symptoms in individuals who had previously experienced COVID-19. Methods: This study was designed as a randomized, double-blind, placebo-controlled trial. A total of 62 participants were randomly allocated to one of two groups: a psychobiotic group (PG; 23 women, 9 men) receiving 3 × 109 CFU Lactobacillus helveticus and Bifidobacterium longum, or a control group (CG; 21 women, 9 men) receiving a placebo, for 6 weeks. Fifty-six participants finalized the study and were included in the analysis (28 per group). The severity of depressive and anxiety symptoms at baseline and after the intervention was assessed using validated self-assessment tools: the Hospital Anxiety and Depression Scale (HADS), the Generalized Anxiety Disorder 7-item scale (GAD-7), the Beck Depression Inventory (BDI), and the Hopkins Symptom Checklist (SCL-90). Additionally, the profile of selected short-chain fatty acids (SCFAs) in the stool was assessed. Results: Following the supplementation period, the PG showed significantly lower median levels of depression and anxiety compared to the CG, corresponding to a 57.2% reduction in anxiety severity (GAD-7) and a 50.9% reduction in depressive symptoms (BDI) (HADS—Depression and Anxiety, and GAD-7: p = 0.0001; BDI: p = 0.0003). Additionally, the prevalence of anxiety and depressive symptoms significantly decreased in the PG compared to the CG based on the HADS-A (p = 0.0044), GAD-7 (p = 0.0219), and BDI (p = 0.0011) scores. Among the measured SCFAs, only the butyric acid concentration in PG increased significantly during supplementation (baseline vs. follow-up—p = 0.0338) and was higher in PG than in CG at the study’s end (p = 0.0248). However, in the PG, changes in the concentrations of all analyzed acids correlated with a reduction in the severity of anxiety symptoms measured using the HADS-A. Conclusions: Psychobiotic supplementation in individuals recovering from COVID-19 who exhibit anxiety and/or depressive symptoms led to mood improvement and a reduction in symptom severity, and it may serve as a supportive treatment.