What Happened to the Original VSL3 Probiotic Formula?

For many years, VSL#3 was the probiotic of choice among Irish gastroenterologists and patients managing conditions including IBD, pouchitis, and IBS. The clinical reputation it held was built on a specific 8-strain blend developed by Professor Claudio De Simone, an Italian microbiologist and clinician. This combination — now formally called the De Simone Formulation (DSF) — was the subject of clinical trials published in Gastroenterology and Gut from 2000 onwards, accumulating over 80 clinical trials and 200 peer-reviewed publications.

In 2016, a commercial separation occurred between Professor De Simone and the VSL#3 brand owner (Actial Srl). The outcome:

• The VSL#3 brand name remained with Actial Srl. The product was subsequently reformulated using different strains from a different cell bank source.
• The original De Simone Formulation remained with its inventor and continued under new brand names across different markets, including Ireland.

A US federal appeals court ruled in 2021 that the product sold as VSL#3 after the split was not the same formulation as the one used in the pre-2016 clinical research.^[1] ECCO issued an official clarification in October 2023 confirming the same position for clinicians and patients across Europe — including Ireland.^[2]

The practical result for Irish consumers: the brand name "VSL#3" and the original De Simone Formulation now refer to two different products. Irish patients who were directed to VSL#3 on the basis of clinical evidence should understand that the guideline evidence relates to the De Simone Formulation, not the current VSL#3 product.

What This Means for People Buying Probiotics in Ireland

Ireland has a well-engaged consumer base for high-potency probiotics, particularly among those managing gut conditions such as IBD, ulcerative colitis, and IBS. Many Irish patients were introduced to high-dose probiotic therapy through the VSL#3 brand, often on the recommendation of a gastroenterologist or GP.

The 2016 commercial split, and the subsequent discontinuation of original Vivomixx 450 in 2025, created real confusion in the Irish market. Consumers ordering probiotics in Ireland who were looking for the clinically-studied formulation faced three products using related branding but with different formulations:

• Current VSL#3: reformulated post-2016, different strains, different cell bank.
• Vivomixx Neo: launched 2024, different formulation from original Vivomixx 450.
• CDS22-formula: the direct formulation continuation of original Vivomixx 450, with the same 8 strains, same DSM codes, same master cell bank.

For Irish consumers who previously used Vivomixx 450 sachets on clinical advice, CDS22-formula is the direct formulation continuation. It is available for delivery across Ireland from Probiotic.ie, the authorised Irish distributor.

Full Timeline: VSL#3 to Vivomixx to CDS22 in Ireland

What ECCO and AGA Guidelines Say — Relevant for Irish Patients and Clinicians

Two major clinical bodies have issued relevant guidance that directly addresses the De Simone Formulation and its relationship to VSL#3. Both are important context for Irish patients and clinicians.

ECCO (European Crohn's and Colitis Organisation)

This is directly relevant to Irish patients who have been referred to "VSL#3" by a gastroenterologist or IBD nurse at an Irish hospital or clinic. If that recommendation was based on clinical guidelines, it relates to the De Simone Formulation — not the current VSL#3 product. The De Simone Formulation is now available in Ireland as CDS22-formula.

AGA (American Gastroenterological Association)

Note: both guidelines reference the De Simone Formulation directly, not a brand name. Irish patients and clinicians using these guidelines to inform product selection should verify that the product used contains the original De Simone Formulation strains and cell bank source — not simply a product that shares a historical brand name.

Strain-Level Comparison: CDS22 vs Current VSL#3 vs Vivomixx Neo

For Irish consumers or clinicians trying to establish formulation equivalence, ECCO's recommended method is strain-level comparison — not brand name. The table below compares the eight strains of the original De Simone Formulation (as found in CDS22-formula, available in Ireland) with the current VSL#3 product and Vivomixx Neo.

Note on the current VSL#3 product: VSL#3 uses some species names that overlap with the De Simone Formulation, but the strain codes differ from the original DSM codes, and the bacterial sources come from a different cell bank. In clinical research, formulation identity is determined by strain code and cell bank source — not by species name alone.

CDS22-formula DSM strain codes from public manufacturer documentation. Current VSL#3 strain codes from publicly available label information. Vivomixx Neo described as a different formulation based on manufacturer materials. Always verify against current manufacturer documentation before making clinical decisions.

How to Verify Formulation Identity Yourself

Rather than relying on brand names or marketing claims, formulation identity can be verified directly using publicly available sources. This is the approach ECCO recommends — and it applies equally to Irish consumers and clinicians.

Which Products Contain the Original De Simone Formulation in Ireland?

VSL3 Alternative Ireland: Common Questions Answered

Further Reading on the De Simone Formulation in Ireland