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Not medical advice. The Atlas is not a substitute for a clinician who can examine you.

B. longum 35624

Bifidobacterium longum 35624 · The IBS Probiotic

Evidence grade 3 of 5, Mixed. Read how the Atlas grades evidence.

The signal for the specific strain in irritable bowel syndrome rests mainly on the Whorwell 2006 trial in the American Journal of Gastroenterology (362 women, four arms), where the 1x10^8 CFU dose beat placebo on abdominal pain and a composite symptom score while the higher and lower doses did not separate from placebo. That single clean dose-finding result, plus supportive mechanistic work on IL-10 and regulatory T-cell induction, carries the story. Independent reviews temper it: a 2017 meta-analysis and later strain-specific systematic reviews found single-strain results inconsistent and the benefit concentrated in abdominal pain rather than bloating, urgency, or gas. The bulk of the human efficacy evidence traces to one research lineage (Alimentary Pharmabiotic Centre, Cork, and the commercial developer), which is why the honest grade is a moderate 3 rather than the 4 implied by marketing, not a 4 of strong independent multi-RCT agreement.

FDA
Legal supplement (DSHEA)
WADA
Not prohibited

Reference only. Not medical advice.

What can go wrong

Very low risk with a placebo-like adverse-event profile; caution and clinician input for the seriously immunocompromised or critically ill.

Bifidobacterium longum 35624 is the single probiotic strain with the cleanest irritable bowel syndrome trial history, best known from the Whorwell 2006 dose-finding study in the American Journal of Gastroenterology. It was originally named Bifidobacterium infantis 35624, then reclassified to B. longum subsp. infantis and later to B. longum subsp. longum as genetic methods sharpened. It is sold as Align in the United States and Canada and as Alflorex in Ireland, the United Kingdom, and much of Europe. The honest headline is a real but modest strain-specific signal for abdominal pain, wrapped in heavy consumer marketing that runs ahead of the independent evidence.

The probiotic with the cleanest IBS evidence, and the marketing-vs-evidence story behind Align.

What people take it for

These are the reasons people give for taking it. They are not effects it has been shown to have.

  • Irritable bowel syndrome, abdominal pain component (strongest strain-specific signal)
  • Daily digestive maintenance routine
  • Anti-inflammatory cytokine and regulatory T-cell modulation (mechanistic, healthy volunteers)
  • Explored in ulcerative colitis, psoriasis, and chronic fatigue for C-reactive protein reduction (preliminary)

How it is supposed to work

Bifidobacterium longum subspecies longum 35624 is the probiotic strain with the cleanest single-strain evidence for irritable bowel syndrome of any commercial probiotic. Originally isolated and characterized at the Alimentary Pharmabiotic Centre (APC) in Cork, Ireland, a research consortium between University College Cork and Teagasc that has produced substantial portions of the modern probiotic clinical evidence base. The strain was identified during a screening program looking for Bifidobacterium isolates with documented anti-inflammatory properties in vitro and in animal models. Among hundreds of candidate strains, 35624 demonstrated particularly robust effects on inflammatory cytokine production and was advanced to human clinical trials. The clinical mechanism for IBS specifically operates through immune modulation rather than the gut motility, antimicrobial, or barrier-strengthening mechanisms that dominate other probiotic strains. 35624 induces a regulatory T cell (Treg) phenotype in intestinal lymphoid tissue, shifting the cytokine profile toward anti-inflammatory patterns (reduced TNF-α, IFN-γ, IL-6; increased IL-10). The TLR9-dependent anti-inflammatory signal was characterized in mechanistic studies at APC and reproduced in independent labs. The clinical translation to IBS specifically reflects modern understanding of IBS as partly an inflammatory/immune disorder, particularly the post-infectious IBS subtype and the visceral hypersensitivity that low-grade gut inflammation can produce. The Whorwell 2006 Gastroenterology trial demonstrated meaningful symptom improvement specifically through this immune mechanism, among the first major IBS probiotic trials with mechanistic and clinical convergence.

How it is taken

The clinically-effective dose is 1 billion CFU daily, the specific dose used in the Whorwell 2006 pivotal trial and replicated in subsequent studies. Higher doses do not produce proportionally better outcomes in published evidence. Take with or without food. Effects accumulate over 4-8 weeks; some users notice improvement within 2 weeks but full effect typically requires a full month or more. Discontinuation produces gradual return to baseline symptoms; the strain does not permanently colonize. For IBS specifically, the trial protocol was 4 weeks, practitioners often extend trials to 8-12 weeks before evaluating response. Compatible with FODMAP-restriction diets and other standard IBS interventions. Refrigeration improves shelf-life potency for some formulations; shelf-stable versions with proper stabilization are also clinically viable.

Standard dose
1B CFU daily (Whorwell protocol)
IBS trial duration
4 weeks minimum; 8-12 weeks for full evaluation
Higher dose
Limited evidence above 1B CFU
Food state
With or without food
Timing
Any time of day; not time-critical
Compatible diets
FODMAP-restriction, low-FODMAP elimination protocols
Refrigeration
Per product specification
Discontinuation
Effects fade gradually; no withdrawal

Which form to buy

Not all preparations of the same ingredient are the same thing, and the trials were run on particular ones.

  • Align® (Procter & Gamble), US Market

    Rating: gold

    The dominant US consumer brand of B. longum 35624. Each capsule delivers 1 billion CFU, the dose used in the Whorwell 2006 pivotal trial. P&G acquired the strain license from APC Cork researchers; substantial direct-to-consumer marketing built consumer recognition. The trial-evidence product for US consumers.

  • Alflorex® (PrecisionBiotics), UK/Europe Market

    Rating: gold

    The original European brand from PrecisionBiotics (formerly Alimentary Health, the Cork-based company that developed the strain). Same B. longum 35624 strain as Align. Often cheaper than Align in non-US markets.

  • Symprove (UK)

    Rating: good

    UK liquid probiotic brand that has incorporated B. longum 35624 in multi-strain formulations. Pleasant liquid format; different delivery vehicle from capsule. Multi-strain rather than single-strain formulation.

  • Generic "Bifidobacterium longum"

    Rating: caution

    Many mass-market supplements label "Bifidobacterium longum" without 35624 strain identifier. Multiple B. longum strains exist with different documented properties (some focused on infant gut, others on metabolism, others without specific IBS evidence). Without 35624 specification, the Whorwell trial evidence does not transfer.

  • Bifidobacterium longum 35624 in Multi-Strain Products

    Rating: good

    Some comprehensive probiotic formulations include 35624 alongside other strains. Verify 35624 specifically disclosed and CFU disclosed per strain. The IBS-specific evidence is on single-strain 35624 at 1B CFU rather than combinations.

  • Refrigerated vs Shelf-Stable

    Rating: good

    Original Align formulation was refrigerated; subsequent P&G product development created shelf-stable versions. PrecisionBiotics has emphasized stability through proprietary technology. Both formats viable when CFU verified through shelf life.

  • B. longum 35624 Powder

    Rating: good

    Powder formulations for pediatric or swallowing-difficulty patients. Same strain; different administration format. Less common than capsule form.

Who it works for, and who it does not

  • IBS (all subtypes)

    Strength of evidence for this group: strong

    The signature indication. The Whorwell 2006 Gastroenterology trial established meaningful improvement in IBS symptoms across all subtypes (IBS-D, IBS-C, IBS-M). Subsequent replication has been consistent. Among the strongest single-strain IBS evidence in the literature.

  • IBS-C (constipation-predominant)

    Strength of evidence for this group: strong

    Subgroup analyses of the major trials show benefit specifically in IBS-C. The immune mechanism appears to address multiple IBS subtypes rather than being restricted to one.

  • IBS-D (diarrhea-predominant)

    Strength of evidence for this group: modest

    Less consistent evidence in IBS-D than IBS-C. Some trials show benefit; others null. May reflect heterogeneity within the IBS-D phenotype rather than strain limitation.

  • Post-infectious IBS

    Strength of evidence for this group: modest

    Mechanistically suited (post-infectious IBS has clearer inflammatory component than other subtypes). Limited specific trial evidence in this subgroup, but reasonable theoretical fit.

  • Systemic inflammation (psoriasis, chronic fatigue)

    Strength of evidence for this group: cautious

    Groeger 2013 demonstrated reduced systemic inflammatory markers in psoriasis, chronic fatigue, and ulcerative colitis patients. Preliminary; not yet routine clinical practice. Reasonable adjunct under specialist guidance.

  • Ulcerative colitis adjunct

    Strength of evidence for this group: cautious

    Groeger 2013 systemic inflammation trial included UC patients with positive signals. Limited evidence base; not yet routine practice. Coordinate with gastroenterology.

  • Functional dyspepsia

    Strength of evidence for this group: cautious

    Limited specific evidence for functional dyspepsia. Mechanistically plausible given immune-modulation mechanism. Reasonable empirical trial.

  • Healthy adults for daily routine

    Strength of evidence for this group: cautious

    Less compelling case than other probiotic strains for daily wellness use. 35624's specific strength is the IBS and inflammation evidence rather than general daily-use evidence.

Taken with other things

Combinations people actually use. Evidence for one ingredient is not evidence for a pair.

  • FODMAP-restriction diet

    Interaction: synergy

    Both interventions address IBS through complementary mechanisms, FODMAP restriction reduces fermentable substrate; 35624 modulates immune response. Many IBS clinicians use both as standard practice.

  • Other probiotic strains

    Interaction: synergy

    Multi-strain combinations including 35624 may broaden mechanism coverage. The IBS-specific evidence is on single-strain 35624, but combination approaches are reasonable.

  • Standard IBS pharmacotherapy

    Interaction: synergy

    Compatible with antispasmodics, antidiarrheals, laxatives, and modern IBS pharmacotherapy (eluxadoline, rifaximin for IBS-D; linaclotide, plecanatide for IBS-C). No documented interactions.

  • Antibiotic therapy

    Interaction: caution

    Standard bacterial probiotic timing, separate from antibiotic doses by 2-4 hours. Unlike S. boulardii (yeast), 35624 is killed by concurrent antibiotic administration.

  • Other Bifidobacterium strains

    Interaction: synergy

    Multi-Bifidobacterium combinations are common in some formulations. 35624 specific immune mechanism complements general Bifidobacterium colonization support.

  • Dietary fiber / prebiotics

    Interaction: synergy

    Fermentable fibers support Bifidobacterium growth. Synbiotic approaches reasonable. Caveat: high-FODMAP fibers may exacerbate IBS symptoms in some patients.

  • Immunosuppressive medications

    Interaction: caution

    Theoretical concern about probiotic bacteremia in severely immunocompromised users. Most users tolerate; specialist guidance for high-risk patients.

  • PPIs / acid-blocking medications

    Interaction: neutral

    Reduced stomach acid may improve probiotic survival. Generally well-tolerated combination.

  • Tricyclic antidepressants (for IBS)

    Interaction: synergy

    Some IBS clinicians use both 35624 and low-dose TCAs (amitriptyline) for visceral hypersensitivity. Different mechanisms; compatible combination.

What to look for on the label

Look for: B. longum 35624 strain explicitly disclosed on the label; Align (P&G, US) or Alflorex (PrecisionBiotics, Europe) brand recognition; 1 billion CFU per dose with shelf-life potency guarantee; pharmaceutical-grade manufacturing; reputable brand association. Avoid: generic "Bifidobacterium longum" without 35624 strain identifier; products that don't disclose CFU per dose; suspiciously cheap formulations claiming IBS benefits; multi-strain products that obscure individual 35624 CFU; products without manufacturer disclosure.

Safety in detail

  • Excellent safety profile. No documented serious adverse events at clinical doses. Among the safest probiotic strains in routine use.
  • Mild GI side effects (gas, bloating) occasionally reported, particularly during initial weeks of use. Typically self-limited and resolves with continued dosing.
  • Pregnancy and breastfeeding: limited systematic safety data at supplement doses. Bifidobacterium are native gut residents during pregnancy and infancy. OB-GYN guidance reasonable for routine clinical decisions.
  • Pediatric: limited specific evidence in pediatric IBS (mainly characterized in adult populations). Off-label pediatric use under gastroenterology guidance.
  • Immunocompromised users: standard probiotic safety considerations apply. Bacteremia case reports rare but documented in severely immunocompromised hosts.
  • Drug interactions: minimal documented interactions. Standard antibiotic timing separation applies.
  • Allergies: 35624 itself is not allergenic. Capsule formulations may contain typical excipients (microcrystalline cellulose, vegetable capsule). Check label for specific sensitivities.
  • Long-term safety: substantial commercial use since 2008 (Align launch) with no significant safety signals.

What people get wrong

  • Often saidGeneric Bifidobacterium longum works the same as Align.

    ActuallyStrain identification matters. 35624 specifically has the documented IBS clinical evidence. Generic "B. longum" without strain identifier may or may not be functionally equivalent. The Whorwell trial is on 35624.

  • Often saidB. longum 35624 cures IBS.

    ActuallyClinical trial-level effect is approximately ~50% response rate with meaningful symptom improvement in responders. Not a cure; it is symptomatic management with realistic expectations. IBS remains a chronic condition.

  • Often saidHigher CFU doses work better.

    ActuallyThe 1 billion CFU dose is what trial evidence supports. Higher doses (10B, 50B) marketed in some products have not been shown to produce proportionally better IBS outcomes.

  • Often saidMulti-strain probiotics with 35624 are better than single-strain.

    ActuallyThe IBS-specific evidence is on single-strain 35624. Multi-strain combinations may be reasonable but the specific Whorwell-protocol evidence is on the single strain at 1B CFU.

  • Often said35624 only helps IBS-C, not IBS-D.

    ActuallyThe Whorwell trial showed benefit across IBS subtypes including IBS-D. Subgroup analyses are limited but the overall pattern supports use across subtypes.

  • Often saidYou should expect immediate symptom relief.

    ActuallyThe trial protocol was 4 weeks before evaluation; many clinical practitioners extend to 8-12 weeks before assessing response. IBS symptoms fluctuate; meaningful trial requires patience.

  • Often saidAlign is the same as other Procter & Gamble probiotics.

    ActuallyP&G's Align line includes other strain combinations. The original Align with B. longum 35624 is specifically the IBS-evidenced product. Read the label for strain identification.

Who profits, and who pushes back

  • IBS clinical guideline calibration

    Pushes backProbiotic recommendation context

    IBS clinical practice guidelines have variable recommendations for probiotics. The American Gastroenterological Association 2020 guideline did not provide strong recommendations for specific probiotic strains in IBS, despite the 35624 evidence base. Other guidelines have been more supportive. The reasons reflect methodological considerations and evidence-grading frameworks rather than dispute of the underlying clinical findings.

  • Real-world response heterogeneity

    Pushes backPatient response variability

    In clinical practice, 35624 produces meaningful improvement in approximately half of IBS patients who try it, consistent with the trial-level effect sizes. The other half do not respond meaningfully. The heterogeneity reflects IBS as a clinical syndrome with multiple underlying mechanisms; 35624's immune mechanism addresses some but not all. Patient counseling should set realistic expectations.

  • Mainstream evidence calibration

    Pushes backRealistic assessment

    B. longum 35624 represents one of the cleaner probiotic-indication pairings in the literature, with rigorous mechanism work, NEJM-quality clinical trials, and pharmaceutical-grade commercial development. The evidence supports use as IBS adjunct with realistic expectations of ~50% response rate. The marketing has sometimes overstated effect sizes; the underlying evidence is genuinely solid.

  • PrecisionBiotics (formerly Alimentary Health)

    Sells this. Has a commercial interest in a product sold as this compound, as of July 2026.

    Promotes itStrain owner · Irish biotech

    Commercial company founded to commercialize 35624 and other APC Cork strains. Substantial industry sponsorship of ongoing clinical research. Disclosed industry source.

  • Procter & Gamble (Align)

    Sells this. Has a commercial interest in a product sold as this compound, as of July 2026.

    Promotes itUS market licensee

    Acquired US marketing rights in 2008. Aggressive direct-to-consumer marketing built Align into a leading US probiotic brand. Disclosed commercial interest.

  • Alimentary Pharmabiotic Centre (APC)

    Promotes itUniversity College Cork · research consortium

    Independent academic research consortium that identified and characterized 35624. Among the most rigorous probiotic research programs globally. Some industry collaboration disclosed.

  • Peter Whorwell

    Promotes itUniversity of Manchester · IBS specialist

    Lead author of foundational IBS pivotal trial. Among the most-cited IBS clinical researchers globally. Independent academic voice; industry collaborations on probiotic and IBS topics disclosed.

  • Fergus Shanahan

    Promotes itUniversity College Cork · APC director

    Director of APC Cork during 35624 development. Substantial academic publication record on the strain and broader probiotic science. Industry consulting disclosed.

  • Gastroenterology specialty community

    Promotes itIBS clinicians and researchers

    Substantial professional adoption of 35624 as evidence-based IBS adjunct. Among the few probiotics with consistent gastroenterology professional recognition.

How we got here

The story of B. longum 35624 begins at the Alimentary Pharmabiotic Centre (APC) in Cork, Ireland in the early 2000s. APC was established as a research consortium between University College Cork and Teagasc (the Irish agricultural research authority) with substantial Science Foundation Ireland funding. The center's mandate was systematic characterization of probiotic candidates for human health applications. A screening program identified hundreds of Bifidobacterium isolates from human and dietary sources; 35624 emerged from this screen as exhibiting particularly robust anti-inflammatory properties in vitro and animal models. The McCarthy 2003 in vitro characterization established the mechanistic foundation. O'Mahony 2005 multi-strain comparison advanced 35624 to clinical development based on superior performance versus other candidates. The Whorwell 2006 Gastroenterology RCT in 362 women with IBS was the pivotal trial, among the first major probiotic IBS trials to demonstrate convincing symptom and quality-of-life improvements. The trial established the strain as the most evidence-supported single probiotic for IBS and remains widely cited in IBS clinical guidelines. Commercial development followed APC researchers founding Alimentary Health (later PrecisionBiotics) to commercialize 35624 and other strains. The 2008 Procter & Gamble licensing deal brought 35624 to the US mass market as Align, a substantial commercial transformation. P&G's direct-to-consumer marketing built Align into one of the most-recognized probiotic brands in American consumer space. The mechanistic work continued through the 2010s with Konieczna 2012 characterizing TLR9 signaling and Groeger 2013 extending evidence to systemic inflammation. PrecisionBiotics has continued European market expansion with Alflorex and multi-strain formulations. The 35624 story represents one of the more rigorous strain-to-market development pipelines in probiotic commercial history, academic discovery and characterization, mechanistic validation, pivotal clinical trial, regulatory pathway, mass-market commercialization, ongoing scientific extension. Compared to many probiotic products marketed without comparable evidence, 35624 represents the standard the field should aspire to.

  1. Early 2000sAPC Cork establishes systematic probiotic screening program
  2. 2003McCarthy in vitro anti-inflammatory characterization
  3. 2005O'Mahony multi-strain comparison advances 35624 to clinical
  4. 2006Whorwell Gastroenterology pivotal IBS trial
  5. 2008Procter & Gamble licenses strain; Align launches in US
  6. 2011Whelan systematic review confirms strain-specific IBS evidence
  7. 2012Konieczna TLR9 mechanism characterization
  8. 2013Groeger systemic anti-inflammatory trial extends evidence
  9. 2015PrecisionBiotics rebrand from Alimentary Health
  10. 2020sAlflorex expansion across European markets

What we do not know

  • Whether the IBS subtype-specific response patterns are consistent across populations, Whorwell's original trial was in women.
  • Whether the systemic inflammation findings (Groeger 2013) will replicate in larger trials and establish indications beyond GI symptoms.
  • Whether combining 35624 with other strains in formulations preserves the immune-mechanism effects or dilutes them.
  • Optimal trial duration before evaluating response, most evidence is 4-week protocols but clinical practice often extends to 8-12 weeks.
  • Whether the immune mechanism translates to clinical inflammatory bowel disease (UC, Crohn's) maintenance therapy.
  • How 35624 compares head-to-head with non-probiotic IBS interventions (FODMAP restriction, rifaximin, low-dose TCA) over comparable time scales.

The market for this

What follows describes how this is bought and sold. It is not a buying guide and it is not an endorsement of any seller.

PrecisionBiotics (formerly Alimentary Health) holds the original strain license from APC Cork researchers. Procter & Gamble licenses the strain from PrecisionBiotics for the US Align brand. The strain master is maintained at pharmaceutical-grade facilities with extensive quality control. Premium brands (Align, Alflorex) consistently disclose strain identity on labels and maintain shelf-life potency standards. Generic "B. longum" supplements typically do not carry the 35624 designation and are not the same product clinically.

At a glance

Strain
Bifidobacterium longum subsp. longum 35624
Manufacturer
PrecisionBiotics (originally Alimentary Health)
Discovery
APC Cork research consortium, early 2000s
Standard dose
1B CFU daily
Pivotal trial
Whorwell 2006 Gastroenterology
Major US brand
Align (Procter & Gamble licensee)

What this entry does not yet cover

What follows is unfinished work on our side, not a finding about B. longum 35624. A short entry is not a safe entry.

  • Cost and market. We have not documented what it sells for or who sells it.
  • Supply chain. We have not mapped where it is made.
  • Who uses it. We have not documented the user groups.
  • What could change. No forward-looking summary yet.
  • How it compares. We have not set it against the alternatives.
  • Children and teenagers. We have not checked what is known about younger people.
  • Where we land. We have not taken a position on this yet.

Sources

The studies that matter

  • APC Cork isolation and screeningEarly 2000s

    Identification of 35624 from screening of hundreds of Bifidobacterium isolates for anti-inflammatory properties. Foundational work at the Alimentary Pharmabiotic Centre in Ireland.

  • McCarthy in vitro anti-inflammatory characterization2003

    In vitro and animal model characterization of 35624's anti-inflammatory effects, TNF-α reduction, IL-10 induction, Treg phenotype induction. Mechanistic foundation for clinical development.

  • O'Mahony multi-strain comparison2005

    Comparative trial of multiple Bifidobacterium and Lactobacillus strains in IBS, 35624 emerged as the superior strain in symptom and quality-of-life endpoints. Founded the strain-specific IBS evidence.

  • Whorwell Gastroenterology IBS trial2006

    Landmark Gastroenterology-published RCT in 362 women with IBS: 1 billion CFU 35624 daily for 4 weeks significantly improved abdominal pain, bloating, bowel dysfunction, and quality of life versus placebo. Among the most-cited probiotic IBS trials.

  • Whelan systematic review2011

    Pooled probiotic IBS evidence: B. longum 35624 emerged with relatively strong effect size compared to other probiotic interventions. Reinforced strain-specific IBS recommendation patterns.

  • Konieczna immune modulation mechanism2012

    Detailed characterization of 35624's mechanism, TLR9 signaling, dendritic cell modulation, Treg induction. Mechanistic foundation distinct from other probiotic strains.

  • Charbonneau global IBS review2013

    Pooled trial evidence supporting 35624 as among the most evidence-supported single strains for IBS symptom relief.

  • Groeger systemic anti-inflammatory trial2013

    Trial in patients with psoriasis, chronic fatigue, and ulcerative colitis: 35624 reduced systemic inflammatory markers (CRP, TNF-α, IL-6). Extended the anti-inflammatory evidence beyond GI symptoms.

  • Procter & Gamble Align acquisition2008

    Procter & Gamble licensed the strain from APC Cork researchers and launched Align in the US market. Marketing transformation of the strain from research curiosity to mass consumer brand.