Healthy bacteria improved depression and anxiety months after COVID-19
STUDY: Drzymala S et al, Metabolites 2026
STUDY TYPE: Randomized, double-blind, placebo-controlled trial
FUNDING: Independent
Background
Probiotics improved anxiety and depression in over two dozen randomized trials. In an earlier randomized trial, they improved fatigue, cough, and well-being in 147 patients with acute COVID-19, and this trial tested them in long COVID.
The trial used Lactobacillus helveticus and Bifidobacterium longum, which are often employed in psychiatric trials.
The Study
- 62 adults with post-COVID anxiety or depression, randomized to a probiotic or placebo daily for 6 weeks; 56 completed
- Assessed with the Hospital Anxiety and Depression Scale, GAD-7, Beck Depression Inventory, and Hopkins Symptom Checklist, plus stool fatty acids
Results
The probiotic group had lower anxiety and depression scores than placebo at 6 weeks, including a 57% drop in anxiety severity (GAD-7) and a 51% drop in depression (BDI). Clinically significant anxiety and depression also fell more with the probiotic.
Butyric acid, a fatty acid linked to gut and brain health, only rose in the probiotic group, a rise that correlated with the anxiolytic effects.
Side Effects
None. There is an outdated notion that probiotics can cause bacterial overgrowth, but newer studies find they prevent that.
Limitations
The small trial excluded severe depression, enrolled a mostly overweight population without a healthy comparison group, and relied on self-reported measures. It didn’t analyze changes in gut microbiota.
Practice Implications
- With only a few trials in COVID, probiotics are preliminary.
- However, their support in other psychiatric disorders (cognition, depression, anxiety, insomnia, autism, and metabolic side effects of antipsychotics) is more robust, so consider them for long COVID in patients with those disorders.
- Find lab-tested brands with the right ingredients for mental health.
—Chris Aiken, MD
Director, Psych Partners
Editor in Chief, Carlat Psychiatry Report
