Michael Hunter, MD on Medika Life

Surprising Link Between Probiotics, Anxiety, and Depression

MAJOR DEPRESSIVE DISORDER (MDD) IS A PREVALENT mental health condition. While clinicians commonly prescribe antidepressant medications for MDD, many do not experience full symptom relief. This essay unveils the surprising link between probiotics, anxiety, and depression.

Persistent sadness, hopelessness, and a loss of interest or pleasure in daily activities characterize MDD.

There has been growing interest in exploring alternative treatment approaches in recent years. These tools include probiotic supplementation to alleviate anxiety and depression symptoms.

A pilot randomized trial published in JAMA Psychiatry provides valuable insights into the potential benefits of probiotic supplementation as an adjunctive treatment for individuals with a major depressive disorder who do not achieve a complete remission with antidepressants.

We will examine the study findings and discuss the implications for clinical practice.

Depression is Common

Major depression is quite common, with around 264 million people globally experiencing this debilitating disorder, according to the World Health Organization.

According to The National Institute of Mental Health, 17.3 million (7.1 percent of adults) have had at least one major depressive episode in the United States.

The National Institute of Mental Health explains that of adults, 17.3 million (7.1 percent of the adult population) have had at least one major depressive episode in the United States.

The prevalence of major depression varies across different countries and populations, but it is a significant public health concern.

Photo by Victoria Volkova on Unsplash

Major depression affects individuals from all walks of life, irrespective of age, gender, socioeconomic status, or cultural background. It is not limited to a specific demographic group and can occur in children, adolescents, adults, and older adults.

Women may be more likely to experience major depression than men. The reasons for this gender difference are not fully understood.

Despite its commonality, major depression is often underdiagnosed and undertreated. Many individuals suffering from depression do not seek professional. Reasons include stigma, lack of awareness, and limited access to mental health services.

Addressing the prevalence of major depression requires increased awareness. We also need improved mental health literacy and enhanced accessibility to appropriate treatments and support systems for those affected.

Depression (major depressive disorder) – Symptoms and causes


Anxiety is common

Anxiety disorders are among the most common mental health conditions worldwide, affecting a significant portion of the global population. The condition is the most common mental illness globally and has a striking impact on the global disease burden.

Anxiety is a normal and adaptive response to stress or danger, but it can be classified as an anxiety disorder when it becomes chronic, excessive, and interferes with daily functioning.

Approximately 284 million individuals experience an anxiety disorder, making it a widespread concern.

It is important to note that anxiety disorders are not exclusive to any particular demographic group and can affect people from all backgrounds and age groups.

Anxiety disorders can manifest in various forms, such as generalized anxiety disorder (GAD), panic disorder, social anxiety disorder, specific phobias, and post-traumatic stress disorder (PTSD).

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Anxiety-related conditions can significantly impact an individual’s quality of life, relationships, and overall well-being.

Similar to major depression, anxiety disorders are often underdiagnosed and undertreated. Many anxious individuals don’t seek professional help due to stigma, lack of awareness, or fear of judgment.

Furthermore, some individuals may not recognize that their distressing symptoms indicate an anxiety disorder. Addressing the prevalence of anxiety requires promoting mental health awareness, reducing stigma, and ensuring access to appropriate diagnosis, treatment, and support services for those in need.

Anxiety disorders – Symptoms and causes


Probiotics, Anxiety, and Depression

The randomized trial investigated the effects of probiotic supplementation as an adjunctive treatment for anxiety and depression symptoms in patients with MDD.

The study included 120 participants already receiving treatment with antidepressant medication but had not achieved full remission.

They were randomly assigned to receive either a widely-available, 14-strain probiotic supplement or a placebo. Subjects took the supplement or placebo four times daily for eight weeks.

Researchers assessed the severity of anxiety and depression symptoms using standardized measures at the beginning and end of the study.

The trial results revealed:

A significant drop in anxiety and depression symptoms among those who received probiotic supplementation (versus a placebo).

This finding suggests that probiotic supplementation may benefit mental health outcomes in individuals with MDD who do not experience complete relief from antidepressants alone.

Importantly, the use of probiotics as an adjunctive treatment did not interfere with the efficacy of the antidepressant medication, emphasizing its potential as a complementary therapeutic approach.

Probiotics mechanism

The mechanisms underlying the observed effects of probiotic supplementation on anxiety and depression symptoms are not yet fully understood.

However, there are several plausible explanations based on current scientific understanding. One hypothesis is that probiotics may modulate the gut-brain axis, bidirectional communication between the gastrointestinal and central nervous systems.

Emerging evidence suggests that alterations in gut microbiota composition and function are associated with mood disorders. Probiotics help restore a healthy balance of gut bacteria, improving mental well-being.

Photo by Nastya Dulhiier on Unsplash

Furthermore, probiotics exert anti-inflammatory effects and regulate the production of neurotransmitters, such as serotonin, which play a crucial role in mood regulation.

Dysfunction in the serotonergic system is implicated in the pathophysiology of anxiety and depression. By influencing serotonin levels, probiotics may help alleviate depressive symptoms and promote a more positive mood state.

Probiotics: What is it, Benefits, Side Effects, Food & Types

Probiotics are a mixture of live bacteria or yeast in your body.


Clinical Trial Implications

The findings of this pilot trial have important implications for clinical practice, particularly for individuals with MDD who do not achieve full remission with antidepressants alone.

Adding probiotic supplementation as an adjunctive treatment may offer a valuable and safe option to enhance therapeutic outcomes. Given probiotics’ relatively low cost and minimal side effects, it could be a feasible and accessible intervention for many patients.

Study Limitations

However, it is essential to recognize the limitations of this study. First, the trial had a relatively small sample size, and we need to interpret the findings cautiously until replicated in larger, more diverse populations.

Secondly, the specific probiotic strain, dosage, and treatment duration used in this trial may not be generalizable to all available probiotic products. We need additional research to identify the most effective probiotic strains and optimal treatment protocols for managing anxiety and depression symptoms in patients with MDD.

Third, adherence was evaluated through capsule count, which, while the most commonly used method in clinical trials, can lead to overreporting.

In conclusion, the pilot randomized trial published in JAMA Psychiatry suggests that probiotic supplementation used as an adjunctive treatment holds promise in reducing anxiety and depression symptoms in patients with a Major Depressive Disorder (MDD) who do not experience full relief from antidepressants alone.

Gut-Brain Axis

The study’s findings support the hypothesis that probiotics may positively influence the gut-brain axis and modulate key neurochemical pathways involved in mood regulation.

Sugar, the Gut, and Obesity: Revealing Findings You Should Know About.


We need more study

Although further research is warranted, these results provide a stepping stone for future investigations in larger populations to establish the efficacy and safety of probiotics as adjunctive treatments for anxiety and depression in MDD.

Incorporating probiotics into the treatment landscape may broaden the options available to clinicians and improve outcomes for individuals struggling with MDD.

The randomized clinical trial used the equivalent colony-forming unit of a single serving of kombucha.

Conflicts of Interest

The Medical Research Council Industrial CASE Ph.D. funded the study. Studentship with ADM Protexin (supplier of the probiotics) as the industry partner and additional support from Freya Green.

Study author Dr. Nikolova has received grants from the Medical Research Council and ADM Protexin during the conduct of the study as well as personal fees from Janssen outside the submitted work.


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Michael Hunter, MD
Michael Hunter, MD
I received an undergraduate degree from Harvard, a medical degree from Yale, and trained in radiation oncology at the University of Pennsylvania. I practice radiation oncology in the Seattle area.

Michael Hunter, MD

I received an undergraduate degree from Harvard, a medical degree from Yale, and trained in radiation oncology at the University of Pennsylvania. I practice radiation oncology in the Seattle area.

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