Probiotics for Depression: What the Science Shows

There is growing interest in the link between gut health, mental health, and the role probiotics might play. Many experts now believe that microorganisms known as ‘psychobiotics’ could help treat depression, anxiety, and chronic stress.

We’ve reviewed the latest research to determine whether there is any truth behind this theory, primarily focusing on probiotics for depression.

Probiotics and Depression

Probiotics are live bacteria that people consume either through food or supplements. They have a variety of potential benefits, including improving mental health. They exert their effects by altering the microbiome, the vast population of microorganisms that inhabit the gut.

Probiotics exert their effects by altering the microbiome, the vast population of microorganisms that inhabit the gut.

The microbiome has a significant influence over the gut-brain axis, the communication channel between the digestive tract and the brain. It involves a combination of neurological, immunological, and hormonal pathways.

The gut-brain axis means that mental health can influence digestive health and vice versa. Therefore, dysbiosis (imbalances in the microbiome) could contribute to the development of conditions like major depressive disorder (MDD).

For example, dysbiosis can increase intestinal permeability, a phenomenon known as leaky gut. This allows gut bacteria to enter the bloodstream and cause inflammation, which is closely associated with MDD.


Furthermore, the digestive tract has its own nervous system and produces various neurotransmitters, including serotonin. Therefore, keeping the digestive system healthy is important for maintaining emotional wellbeing. Good nutrition plays a vital role in this, but probiotics could provide additional benefits.

Let’s take a closer look at some of the latest research on probiotics for mental health.

Probiotics for Anxiety & Depression

There is an ever-expanding body of research regarding probiotics for depression and anxiety. Several systematic reviews suggest that they might be useful, although further studies are warranted in certain areas.

A 2016 review found that probiotics had positive effects in both animal and human studies. As well as mitigating leaky gut, they appeared to reduce the impact of stress and improve neurotransmitter levels.

A 2017 review supported these results. It found that probiotics reduced stress-related hormone changes and increased participants’ levels of beneficial neurochemicals, including:

  • Brain-derived neurotrophic factor (BDNF)
  • Gamma-aminobutyric acid (GABA)
  • Tryptophan, the precursor to serotonin and melatonin

In their discussion, the authors of the paper stated: “… it is likely that daily consumption of a probiotic supplement could have a positive effect in improving the mood, anxiety, and cognitive symptoms present in MDD.”

But while these papers suggest that probiotics may benefit MDD, the evidence regarding anxiety is less robust.

For example, a 2020 review found that probiotics significantly improved depression scores compared to placebo. However, there was no significant difference in anxiety scores between the probiotic and placebo groups.

An earlier 2018 review found that although probiotics appeared to reduce anxiety in animal studies, these effects did not translate to humans. The reason for this disparity is unclear, meaning that further research may be necessary.

Probiotics Depression Treatment

Despite the studies’ encouraging results, it is a stretch to suggest that probiotics cure depression. It is even less likely that individuals will see anxiety cured with probiotics.

Individuals with either condition should continue with standard care, such as talking therapies and FDA-approved medication. It is best to view probiotics as an add-on therapy rather than an alternative, and those wishing to stop taking antidepressants should consult their physician.


It is also essential to choose probiotic supplements carefully. The market is poorly regulated and, therefore, many available products are low-quality. They may contain insufficient levels of beneficial microorganisms or, worse still, be contaminated with harmful ones.

Consumers should pay attention to features such as colony-forming units (CFU) and the specific bacterial strains included. The most beneficial options include Bifidobacterium and Lactobacillus strains.

To learn more about choosing a safe and effective supplement, check out our guide: Best Probiotics: Our Top Picks.

It is also important to eat a balanced diet, including plenty of prebiotics. These are substances that ferment in the gut to enhance probiotics’ effects. The best sources of prebiotics are fruit and vegetables.

Probiotics Side Effects

Humans have safely consumed probiotics for thousands of years. The ancient Greeks and Romans recommended eating cheese and fermented foods, while products like kombucha and kimchi became mainstays of Asian cuisine.

Throughout many centuries of probiotic consumption, very few problems have come to light. However, there are some possible side effects for people who are severely ill or have compromised immunity.

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The potentially negative effects of probiotics include:

  • Increased risk of infections
  • The production of potentially harmful substances in the gut
  • Transfer of antibiotic resistance genes to other microorganisms

Therefore, individuals should carefully weigh up the potential benefits and risks before commencing probiotic treatment. 

Final Thoughts on Probiotics for Depression

Research suggests that probiotics could be helpful as an adjunctive treatment for depression. They may counter the negative impact of stress, improve neurotransmitter levels, and reduce inflammation. Moreover, they are generally considered safe for healthy individuals, providing a quality product is selected.

Research suggests that probiotics could be helpful as an adjunctive treatment for depression.

Unfortunately, probiotics appear to provide fewer benefits for people living with anxiety. Although animal studies have shown some anti-anxiety effects, they do not seem to offer the same benefits for humans. Further research is necessary to discover why this is the case.

Anyone interested in trying probiotics for depression and anxiety should continue with their regular treatment unless their doctor advises otherwise. Individuals should also take care to avoid low-quality supplements that may do more harm than good.

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