8 Probiotic Strains That Support Mental Health (The Psychobiotics)

Psychobiotics — probiotics that have specific, documented effects on brain function and mental health — represent one of the most exciting frontiers in integrative psychiatry. The gut-brain axis means that the bacteria in your intestinal tract are directly communicating with your brain through multiple pathways: the vagus nerve, immune signaling, and neurotransmitter precursor production. Here are eight probiotic strains with the most compelling evidence for mental health support.

1. Lactobacillus rhamnosus JB-1

L. rhamnosus JB-1 is one of the most studied psychobiotic strains, with landmark research from the Cryan lab at University College Cork demonstrating that oral supplementation in mice significantly reduced anxiety behaviors and altered GABA receptor expression in the brain — effects that were eliminated by vagotomy, confirming the vagus nerve as the communication pathway. Human studies have shown L. rhamnosus JB-1 to reduce stress hormone (cortisol) levels and improve psychological wellbeing. It appears to work primarily through modulation of GABA signaling — the brain’s primary inhibitory neurotransmitter — producing anxiolytic effects comparable to modest doses of benzodiazepines in animal models. It also reduces intestinal permeability and has anti-inflammatory effects. This is the strain I most commonly recommend for anxiety with gut involvement.

2. Lactobacillus helveticus R0052 + Bifidobacterium longum R0175

This two-strain combination — studied together under the trade name Probio’Stick and Cerebiome — has some of the strongest human clinical trial evidence in the psychobiotic field. A 2011 randomized controlled trial in Brain, Behavior, and Immunity found that healthy volunteers receiving this combination showed significantly reduced psychological distress, including measures of depression, anger, hostility, anxiety, and problem-solving — compared to placebo. Urinary free cortisol was also significantly lower. A follow-up study in patients with irritable bowel syndrome (IBS) found improvements in both gut symptoms and psychological wellbeing. This combination is now included in several high-quality commercial probiotics specifically formulated for stress and mood support, and is the combination I most often recommend for depression and stress in my patients.

3. Bifidobacterium longum

B. longum is among the most extensively studied gut microbiome members, and multiple strains have demonstrated benefits for mental health. Beyond the R0175 strain discussed above, B. longum 1714 has been shown in human clinical trials to reduce perceived stress and cold cognition (negative self-evaluation), improve sleep quality, and reduce salivary cortisol. B. longum helps regulate the immune response, reducing pro-inflammatory cytokines, and produces short-chain fatty acids that support gut barrier integrity and serve as energy sources for colonocytes. Bifidobacterium species are also among the primary fermenters of dietary fiber and producers of acetate and lactate — metabolites with documented effects on brain signaling. B. longum tends to be depleted in modern microbiomes due to antibiotic use, C-section delivery, and formula feeding.

4. Lactobacillus plantarum

L. plantarum is a highly versatile and resilient Lactobacillus species with documented effects on mood, gut barrier function, and inflammation. Clinical trials have found L. plantarum supplementation to reduce depression and anxiety scores in healthy volunteers and to improve cognitive function markers. A 2019 study in Nutrients found that L. plantarum JYLP-326 reduced anxiety and depression scores significantly more than placebo in participants with chronic fatigue. L. plantarum is one of the dominant species in many traditional lacto-fermented foods (kimchi, sauerkraut, traditional pickles) — and regularly eating these fermented foods provides L. plantarum along with a broad array of complementary strains. It is known for its ability to adhere to intestinal epithelium and competitively exclude pathogens, supporting gut barrier integrity.

5. Bifidobacterium breve

B. breve has shown promising results for anxiety reduction and stress response modification in clinical research. A series of studies by Morishita and colleagues found that B. breve A-1 (Mentalibiotics) significantly reduced anxiety and stress responses in healthy adults in randomized controlled trials. Another study found benefits for academic exam stress — a particularly relevant model for common stressors. B. breve is a dominant species in the infant microbiome and tends to decline significantly in adulthood, particularly with westernized diets. It produces short-chain fatty acids, modulates the immune system toward anti-inflammatory phenotypes, and appears to communicate with the brain through the vagus nerve and immune pathways. B. breve is commonly found in high-quality multi-strain probiotic products and in some specialty psychobiotic formulations.

6. Lactobacillus acidophilus

L. acidophilus is one of the most well-known and widely used probiotic strains, with broad effects on gut health and immune function. For mental health specifically, L. acidophilus is relevant for its role in reducing intestinal inflammation and permeability, supporting serotonin precursor availability, and modulating immune signaling. Research has found that L. acidophilus reduces LPS (bacterial endotoxin) production and translocation — directly addressing the gut-to-brain inflammatory pathway most implicated in depression. A study in Molecules found that L. acidophilus combined with B. longum significantly reduced depression and anxiety scores in clinical populations. L. acidophilus is also important for lactose digestion, vaginal health, and preventing antibiotic-associated diarrhea. It is widely available and found in most quality multi-strain products.

7. Bifidobacterium infantis

B. infantis — particularly the 35624 strain — has been extensively studied for its effects on the immune system and on the gut-brain axis. Originally studied for IBS, B. infantis 35624 was shown in clinical trials to reduce pro-inflammatory cytokines (including IL-6 and TNF-alpha) and to increase anti-inflammatory markers — including regulatory T cells and IL-10. Given the cytokine hypothesis of depression (that inflammatory cytokines are primary drivers of many cases of depression), this anti-inflammatory profile makes B. infantis particularly interesting for mood disorders with inflammatory features. B. infantis also plays a role in tryptophan metabolism — influencing whether tryptophan is directed toward serotonin synthesis or toward the pro-inflammatory kynurenine pathway. It is found in many pediatric and adult probiotic formulations.

8. Multi-Strain Probiotic Combinations

While individual strain research is valuable for understanding mechanisms, clinical practice and emerging evidence suggest that multi-strain probiotic products — combining 5–15 clinically relevant strains — may produce superior and broader effects than single-strain supplements. A 2019 meta-analysis in General Psychiatry found that multi-strain probiotics produced larger effect sizes for depression and anxiety reduction than single-strain products. The rationale is ecological: the gut microbiome is a complex ecosystem of thousands of species, and diverse strain supplementation more effectively promotes overall microbiome resilience and diversity. Key strains to look for in a quality psychobiotic multi-strain product: at least one each of Lactobacillus helveticus, Bifidobacterium longum, L. rhamnosus, L. plantarum, and B. breve. CFU counts of 15–50 billion per capsule, with third-party verification of strain identity and potency, are reasonable quality benchmarks.

Choosing the right probiotic for mental health support is not one-size-fits-all — it depends on your specific gut microbiome, symptoms, and health history. At drlewis.com, I help patients navigate the psychobiotic landscape with evidence-based, personalized recommendations as part of a comprehensive integrative psychiatric plan. Brooklyn and telehealth available.