Written and medically reviewed by Dr Zeeshan Afzal (MBBS) — Medical Doctor & Medical Content Lead, Welzo
Evidence-based · Honest about what's proven and what isn't · UK-focused
Last updated: July 2026 · Reading time: ~9 minutes
Bio-Kult's flagship contains 14 strains. OptiBac's typically contain three, at doses that look almost modest by comparison. Neither is being careless — they're following two genuinely different philosophies, and knowing which one you want settles the choice in about a minute.
OptiBac For Women |
OptiBac For Those On Antibiotics |
OptiBac Every Day + FOS |
Availability note: at the time of writing the full OptiBac range at Welzo — all 15 products — is showing as out of stock. Prices below are the listed prices. Check the listing for current availability before planning a purchase.
Table of contents
Almost every probiotic on the UK market sits somewhere on a single spectrum, and these two brands mark its opposite ends.
OptiBac builds products around named strains matched to a specific purpose. Three strains, catalogue-referenced, at a dose chosen to reflect the research on those strains — with a different product for each situation.
Bio-Kult builds products around breadth. Fourteen live bacterial cultures in its flagship, on the reasoning that a healthy gut hosts hundreds of species and a supplement should reflect that complexity.
Both arguments are defensible. They just answer different questions — the trade-off we set out in single vs multi-strain probiotics.
What stands out across the OptiBac range is that every product names its exact strains with catalogue designations. That's unusual, and it's the single most useful thing a probiotic label can do, because probiotic evidence is strain-specific.
| Product | Named strains |
|---|---|
|
For Women, 30 caps £20.01 · 102 reviews |
L. rhamnosus GR-1®, L. reuteri RC-14®, L. paracasei F-19® — 2.5 billion CFU |
|
For Those On Antibiotics, 10 caps £10.10 · 116 reviews |
L. rhamnosus Rosell-11, L. helveticus Rosell-52, B. longum Rosell-175 |
|
For Pregnancy, 30 caps £23.01 · 94 reviews |
L. rhamnosus HN001, L. acidophilus La-14, B. lactis HN019 |
|
For Travelling Abroad, 20 caps £17.10 · 110 reviews |
Saccharomyces boulardii plus three bacterial strains — shelf stable |
|
For Cholesterol, 30 servings £22.80 · 96 reviews |
L. plantarum CECT 7527, 7528, 7529, with 300mg plant omega-3 |
The GR-1 and RC-14 pairing is the clearest example of the philosophy — it is among the better-researched strain combinations for vaginal and urinary health, and OptiBac has built a product around exactly that pairing rather than burying it in a blend.
Two further points in the range's favour: the travel product uses Saccharomyces boulardii, a yeast unaffected by antibacterials, which is the correct organism for that job. And most products are vegan, dairy-free and gluten-free in HPMC capsules — see dairy-free probiotics.
Bio-Kult's flagship is Everyday (previously Advanced Multi-Strain Formulation), a 14-strain capsule at £38.03 for 120 capsules — with multibuy pricing down to £34.23 each on four or more. That's a four-month supply at one a day, which makes the per-day cost competitive despite the headline figure.
The rationale is ecological: your gut hosts hundreds of species, so a supplement supplying fourteen covers more ground than one supplying three. The range also includes symptom-focused variants alongside the everyday formula.
Bio-Kult products are shelf stable, needing no refrigeration — genuinely practical, and covered in shelf-stable probiotics.
An OptiBac product at 2.5 billion CFU sitting beside a competitor advertising 50 billion looks under-dosed. It usually isn't.
Strain-specific products are dosed to reflect the amount used in research on those strains, not to win a numbers comparison. In the best dose-ranging trial in this field, a Bifidobacterium strain improved IBS symptoms at one dose and failed to beat placebo at a dose a hundred times higher. Higher is not automatically better — see CFU vs AFU.
A modest dose of a strain you can look up beats an impressive total of organisms you can't.
| Feature | OptiBac | Bio-Kult |
|---|---|---|
| Philosophy | Targeted, strain-specific | Broad-spectrum coverage |
| Typical strain count | Three | Fourteen in the flagship |
| Strain designations published | Yes — consistently | Check the specific pack |
| Product range | One per situation | Everyday plus variants |
| Formats | Capsules, sachets, gummies, baby drops | Mainly capsules |
| Refrigeration | Not required | Not required |
| Best for | A specific goal | General daily coverage |
A small point, but this article is about strain-level detail, so it belongs here.
The listing for OptiBac For Those On Antibiotics currently describes Bifidobacterium lactis Lafti B94 in one place and lists Bifidobacterium longum Rosell-175 in its ingredients. Those are different organisms. We've used the ingredients list in the table above, since that is the regulated field, and we've flagged the inconsistency for correction.
The general lesson applies to any brand: when body copy and the ingredients panel disagree, trust the ingredients panel — and treat the discrepancy as a reason to check the physical pack.
Both brands are well tolerated by most people. Wind and bloating in the first week or two are common and usually settle — see probiotic side effects.
Speak to a doctor before taking either if you
If you are taking a probiotic during antibiotics, take the two a few hours apart. More in probiotics safety.
On labelling: probiotics carry no authorised health claim in GB or the EU. Both brands are sold as food supplements and cannot legally be marketed as treating any condition.
See your GP — or seek urgent care — if you have:
Switching brands is not the answer to symptoms that aren't improving. See when to see a GP and bowel cancer screening.
Neither is better overall — they follow different philosophies. OptiBac builds targeted products around a few named strains; Bio-Kult builds broad multi-strain blends. Choose OptiBac if you have a specific goal, Bio-Kult if you want general coverage.
Because it doses specific strains at levels reflecting the research on them. Probiotic evidence is strain-specific, so three well-chosen organisms at a studied dose can be more purposeful than fourteen at unknown quantities.
It can be. Trials have found strains effective at modest doses, and one well-known study found a strain worked at one dose and failed at a dose a hundred times higher. Matching the studied dose matters more than maximising the number.
Not automatically. Evidence doesn't stack — a blend of studied strains isn't a studied product unless the blend itself was tested. Breadth is a reasonable hedge when you have no specific target, not a guarantee of more benefit.
OptiBac's antibiotics product is built for that situation with named strains. Whichever you use, take it a few hours apart from the antibiotic.
OptiBac's travel formula, because it includes Saccharomyces boulardii — a yeast, so unaffected by antibacterials — and is shelf stable.
No. Both brands are formulated to be shelf stable, which makes them practical for travel and everyday storage.
Many OptiBac products are stated as vegan, dairy-free and gluten-free in HPMC capsules. Check the individual pack, as it varies across both ranges.
There's no safety reason not to, but little point. If you're combining a targeted product with a broad blend, you won't know which is doing anything.
Allow at least four weeks of consistent use before judging either. See how long probiotics take to work.
Medical disclaimer: This article is for general information and education only and does not constitute medical advice, diagnosis or treatment. Food supplements are not a substitute for a varied and balanced diet, and are not intended to diagnose, treat, cure or prevent any disease. Probiotic effects are strain-specific; evidence for one strain does not transfer to other strains or to blends containing that strain unless the blend itself has been studied. Strain listings are reported from product listings at the time of writing — always check the physical pack, and where product copy and the ingredients panel differ, rely on the ingredients panel. Probiotics should be discussed with a doctor before use if you are immunocompromised, critically unwell, have an indwelling venous line, or have inflammatory bowel disease; yeast-containing products carry an additional caution for people with central venous catheters. Products marketed for pregnancy should still be discussed with a midwife or GP. Severe or bloody diarrhoea during or after antibiotics requires medical assessment. Prices and availability are correct at the time of writing and may change.
About the author
Dr Zeeshan Afzal (MBBS) is a practising medical doctor and Welzo's Medical Content Lead. He writes and reviews Welzo's health content to ensure it is accurate, evidence-based and aligned with current UK clinical guidance.
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