tuneTypical Dose
About 10^8 to 10^9 CFU (100 million to 1 billion) daily. Most commercial products deliver 10^9 CFU per capsule, which is consistent with the Sabaté 2022 observational study for strain 35624
Microbiome Modulator
Bifidobacterium longum
Bifidobacterium longum
Evidence TierCWADA NOT PROHIBITED
watchEffect Window
Some symptom improvement may be noticed within 2 weeks, but meaningful IBS symptom assessment requires at least 4 weeks. Systematic review data suggests extended courses up to 3 months may provide stronger effects.
check_circleCompliance
WADA NOT PROHIBITED
Overview
Clinical Summary
Bifidobacterium longum is a commensal gut bacterium with strain-specific evidence for IBS symptom relief, while stress and cognition signals remain exploratory and strain-specific.
B. longum is one of the most abundant Bifidobacterium species in the adult human gut. The strain with the strongest clinical evidence is B. longum subsp. longum 35624 (formerly classified as B. infantis 35624), which has demonstrated meaningful IBS symptom relief in a well-powered dose-ranging RCT and consistent real-world data. A separate strain, B. longum 1714, has preliminary evidence for stress-response modulation, and newer post-stroke cognition data involve yet another strain, OLP-01. Multi-strain pediatric ADHD data are even harder to attribute. Safety is excellent across studied strains. The most important practical point is strain specificity. Different B. longum strains have different evidence profiles, and choosing a product verified to contain a studied strain matters more than simply taking any B. longum supplement.
B. longum colonizes the large intestine, ferments dietary carbohydrates to produce acetate and lactate, lowers luminal pH to inhibit pathogen growth, competes for epithelial adhesion sites, and strengthens the gut barrier. Strain 35624 specifically modulates T-regulatory cell responses and normalizes the IL-10/IL-12 cytokine ratio in IBS patients, reducing low-grade immune activation that contributes to visceral hypersensitivity. Strain 1714 may modulate the gut-brain axis through vagal signaling, though human evidence for this mechanism is preliminary.
Outcomes
What This Is Expected To Influence
Primary Outcomes
- Reduced IBS symptom severity including abdominal pain, bloating, bowel dysfunction, and gas (strain 35624)
- Improved IBS quality of life scores (strain 35624)
Secondary Outcomes
- Attenuated cortisol and subjective anxiety responses to acute stress (strain 1714, preliminary)
- Normalization of pro-inflammatory to anti-inflammatory cytokine ratio in IBS (strain 35624, mechanistic)
Safety
Contraindications and Interactions
Contraindications
- Critical illness or ICU admission
- Severe immunocompromise
- Short bowel syndrome
- Known allergy to product excipients
Side effects
- Mild gas or bloating
- Transient change in stool consistency
Interactions
- Antibacterial antibiotics
Avoid if
- Critically ill, in the ICU, or severely immunocompromised
- Taking broad-spectrum antibiotics without the ability to separate doses by at least 2 hours
- The product label does not specify a studied strain (35624 or 1714)
Evidence
Study-level References
blong-SRC-001Multicenter, randomized, double-blind, placebo-controlled, dose-ranging trial
Sourceopen_in_newWhorwell PJ, Altringer L, Morel J, et al. Efficacy of an encapsulated probiotic Bifidobacterium infantis 35624 in women with irritable bowel syndrome. Am J Gastroenterol. 2006;101(7):1581-1590.
Population: Women meeting Rome II criteria for IBS recruited from 20 primary care centers in the United Kingdom (n=362)
Dose protocol: Freeze-dried encapsulated B. infantis 35624 at 10^6, 10^8, or 10^10 CFU vs placebo daily for 4 weeks in women with IBS.
Key findings: Only the 10^8 CFU dose significantly reduced abdominal pain and composite IBS symptom scores vs placebo. Both lower and higher doses failed to separate from placebo.
Notes: Landmark dose-ranging trial. Industry-sponsored but well-designed. The non-linear dose-response is an important finding for probiotic dosing.
Paper content
Landmark dose-ranging RCT establishing that B. infantis 35624 (now B. longum subsp. longum 35624) at 1x10^8 CFU daily significantly reduces abdominal pain, bloating, bowel dysfunction, incomplete evacuation, straining, and gas in women with IBS compared with placebo. The study is notable for demonstrating a clear dose-response relationship where only the middle dose (1x10^8 CFU) was effective, while both lower (1x10^6) and higher (1x10^10) doses failed to separate from placebo. This non-linear dose-response has been attributed to potential immunological overstimulation at the highest dose and insufficient colonization at the lowest dose. The trial recruited across all IBS subtypes and used rigorous daily symptom capture. It remains one of the most frequently cited strain-specific probiotic trials in the IBS literature.
blong-SRC-002Prospective, open-label, multicenter observational study
Sourceopen_in_newSabaté JM, Iglicki F. Effect of Bifidobacterium longum 35624 on disease severity and quality of life in patients with irritable bowel syndrome. World J Gastroenterol. 2022;28(7):732-744.
Population: Patients with IBS according to Rome IV criteria enrolled by private practice gastroenterologists in France (n=278 enrolled, n=233 analyzed)
Dose protocol: B. longum 35624 at 10^9 CFU daily for 30 days in IBS patients (Rome IV) in routine gastroenterology practice.
Key findings: IBS severity decreased significantly. 57% of patients moved to a lower severity category or remission. Quality of life improved.
Notes: Valuable real-world data but limited by open-label single-arm design. Consistent with earlier RCT findings.
Paper content
Large real-world observational study confirming that B. longum 35624 at 1x10^9 CFU daily for 30 days reduces IBS severity and improves quality of life. Of the 233 patients analyzed, 57% moved to a lower IBS severity category or reached remission. The study is valuable for demonstrating effectiveness in routine gastroenterology practice rather than only in controlled research settings. However, the open-label single-arm design without placebo control is a significant limitation. IBS has a well-documented high placebo response rate (30-40%), so part of the observed improvement could reflect natural symptom fluctuation, placebo response, or regression to the mean. Despite these caveats, the consistency of results with earlier blinded RCTs on the same strain adds to the weight of evidence for B. longum 35624 in IBS.
blong-SRC-003Randomized, double-blind, placebo-controlled, crossover trial
Sourceopen_in_newAllen AP, Hutch W, Borre YE, et al. Bifidobacterium longum 1714 as a translational psychobiotic: modulation of stress, electrophysiology and neurocognition in healthy volunteers. Transl Psychiatry. 2016;6(11):e939.
Population: Healthy male volunteers (n=22) who completed cognitive assessments, resting EEG, and a socially evaluated cold pressor test
Dose protocol: B. longum 1714 at 10^9 CFU daily for 4 weeks in healthy male volunteers (crossover design).
Key findings: Attenuated cortisol and subjective anxiety during stress challenge. Reduced daily perceived stress. Subtle improvements in visuospatial memory.
Notes: Proof-of-concept psychobiotic study. Small sample (n=22), all male, not yet replicated in clinical populations.
Paper content
First human translational study testing whether preclinical stress-buffering effects of B. longum 1714 could be replicated in healthy volunteers. Using a crossover design, 22 healthy men received B. longum 1714 or placebo for 4 weeks each. Compared with placebo, B. longum 1714 attenuated cortisol output and subjective anxiety in response to the socially evaluated cold pressor test. Daily perceived stress was also lower during the probiotic phase. There were subtle improvements in visuospatial memory and enhanced frontal midline EEG mobility, suggesting a shift in neural processing. This study is important as proof-of-concept that a specific B. longum strain can modulate stress physiology and neurocognition in healthy humans. However, the sample size is small (n=22), participants were all male, and effect sizes were modest. It provides mechanistic credibility for the gut-brain axis concept but does not yet constitute strong clinical evidence for anxiety or mood treatment.
blong-SRC-004Single-blinded, randomized, placebo-controlled trial
Sourceopen_in_newLin ST, Tung TH, Lin YN, Chang FH, Lian YZ, Lai CH, Liou TH, Huang CC, Chen YL, Chao JCJ. Effect of Bifidobacterium longum on cognition and microbiota in post-stroke patients: a single-blinded, controlled trial. Int J Med Sci. 2026;23(3):1058-1069. doi:10.7150/ijms.124024. PMID:41799757.
Population: Post-stroke patients recruited for cognitive and microbiota outcomes.
Dose protocol: B. longum OLP-01 at 2 x 10^10 CFU daily for 12 weeks in 22 post-stroke patients.
Key findings: Improved MoCA, Trail-Making Test, and Stroop test accuracy versus placebo. Gut microbiota composition also altered. Physical performance not affected.
Notes: Extends B. longum cognitive evidence to a clinical population (post-stroke). Very small sample, single-blinded, uses a different strain (OLP-01) than the better-studied 35624 or 1714.
Paper content
This small single-blinded RCT in 22 post-stroke patients found that 12 weeks of Bifidobacterium longum OLP-01 at 2 x 10^10 CFU/day improved cognitive function measures including MoCA scores, Trail-Making Test completion times, and Stroop test accuracy compared to placebo. Gut microbiota composition was also altered in the probiotic group. Physical performance was not significantly affected, suggesting the cognitive benefits may operate through gut-brain axis pathways rather than general nutritional improvement.
blong-SRC-005Triple-blind, randomized controlled trial
Sourceopen_in_newParhiz A, Samani P, Kamali M, Shekari Y, Naghshi N, Faghihshojaei N, Tejareh F, Lahiji NP, Nori A, Aminifard A, Bahmani P, Doaei S, Rabipour F, Gholamalizadeh M. Probiotic Supplementation and Executive Function in Children With Attention-Deficit/Hyperactivity Disorder. Neuropsychopharmacol Rep. 2026;46(1):e70084. doi:10.1002/npr2.70084. PMID:41450035.
Population: Children diagnosed with attention-deficit/hyperactivity disorder.
Dose protocol: Multi-strain probiotic (L. acidophilus, B. lactis, B. longum) once daily for 2 months in 84 children with ADHD.
Key findings: Significantly improved executive function scores (BRIEF) versus placebo (F=7.93, P<0.001).
Notes: Multi-strain product limits attribution to B. longum alone. Adds to the emerging gut-brain axis evidence for Bifidobacterium species in neurodevelopmental contexts.
Paper content
This triple-blind RCT in 84 children with ADHD found that a multi-strain probiotic containing Lactobacillus acidophilus, Bifidobacterium lactis, and Bifidobacterium longum significantly improved executive function scores after 2 months compared to placebo. The probiotic group showed lower (better) BRIEF scores, suggesting potential for probiotics as adjunctive therapy in ADHD. The multi-strain formulation limits attribution to any single species.