How do I know which probiotic strain to take?

Match the strain to your goal. For IBS, look for B. infantis 35624 or L. plantarum 299v. For antibiotic recovery, S. boulardii or L. rhamnosus GG. For general health, a multi-strain product from a reputable brand. Avoid products that don't list specific strain designations.

Should I take probiotics with antibiotics?

Yes — taking S. boulardii or L. rhamnosus GG alongside antibiotics significantly reduces antibiotic-associated diarrhoea risk. Take the probiotic 2-3 hours apart from the antibiotic dose, and continue for 2-4 weeks after finishing the antibiotic course.

How long does it take for probiotics to work?

Most clinical studies show effects within 2-4 weeks of daily use. Some benefits (like reduced antibiotic-associated diarrhoea) appear within days. If you don't notice any benefit after 8 weeks of consistent use, the strain may not be right for you — try a different formulation.

For most UK adults, probiotics are very safe. They are not recommended for people with severely compromised immune systems or short bowel syndrome without medical supervision. S. boulardii is a yeast and is safe for people with bacterial overgrowth conditions.

Do probiotics need to be refrigerated?

Some do, some don't. Refrigeration extends shelf life for most products. Shelf-stable formulations (using freeze-drying and moisture-resistant packaging) are fine at room temperature. Check the label and follow storage instructions.

Can I take probiotics long-term?

Yes — long-term daily use is safe and well-studied. Many UK buyers take probiotics year-round for general gut health, or seasonally for winter immune support.

Probiotics UK Guide: Strains, CFU & Top Products

Last updated: 2026-08-31 · by Sun Supplements

Probiotics are one of the most-searched UK supplement categories, but the details matter — strain, CFU, formulation, and timing all affect results. This guide explains which strains work for which goals, how to read CFU counts, and which UK products are worth buying.

Why probiotics matter for gut health

The gut microbiome — the trillions of bacteria, yeasts, and other microorganisms in your digestive system — influences far more than digestion. Research links microbiome health to immune function, mental health (the gut-brain axis), skin conditions, metabolic health, and even sleep quality. A disrupted microbiome is implicated in IBS, IBD, anxiety, depression, and many chronic inflammatory conditions.

Probiotic supplements deliver specific strains of beneficial bacteria to support or restore microbiome balance. The strongest UK clinical evidence supports probiotics for:

IBS symptom relief — bloating, gas, abdominal pain, irregular bowel movements
Antibiotic-associated diarrhoea — taking probiotics during and after antibiotic courses significantly reduces diarrhoea risk
Infectious diarrhoea — Saccharomyces boulardii is the most-studied strain
Infant colic and eczema prevention — specific Lactobacillus strains
Immune support — particularly in winter

Strains matter: not all probiotics are equal

Unlike most supplements where the active ingredient is well-defined (magnesium is magnesium), probiotics are defined by strain. Two products labelled "Lactobacillus rhamnosus" might be completely different organisms if they use different strains (e.g. LGG vs GR-1). Strain-specific research matters.

The best-studied probiotic strains include:

Lactobacillus rhamnosus GG (LGG) — gold-standard strain for antibiotic-associated diarrhoea and gut immunity
Saccharomyces boulardii — a beneficial yeast (not bacteria), excellent for traveler's diarrhoea and antibiotic-associated diarrhoea
Bifidobacterium lactis HN019 — gut transit time and IBS support
Lactobacillus acidophilus NCFM — general digestive and immune support
Bifidobacterium longum 35624 (Align) — IBS symptom relief
Lactobacillus plantarum 299v — IBS-related bloating

When buying a probiotic, look at the strain designation (not just species) on the label. Premium brands like NOW Foods, Life Extension FLORASSIST, and Jarrow Formulas specify strains.

CFU explained

CFU (colony-forming units) is the count of viable bacteria in each dose. Higher isn't always better — the optimal dose depends on the strain and the goal.

CFU per dose	Typical use
1-5 billion CFU	General maintenance, sensitive individuals
5-25 billion CFU	Standard therapeutic dose for most goals
25-100 billion CFU	Higher-dose therapeutic for IBS, antibiotic recovery, dysbiosis
100+ billion CFU	Severe dysbiosis, under practitioner supervision

UK buyers often assume more is better. The reality: strain specificity and quality of manufacturing matter more than raw CFU count. A 5 billion CFU dose of well-characterised, properly stored, multi-strain product is likely more effective than 100 billion CFU of poorly characterised product.

When and how to take probiotics

Most probiotic research uses doses taken with meals or just before meals. The food buffer protects the bacteria from stomach acid. Take your probiotic:

With breakfast or another substantial meal
30 minutes before a meal on an empty stomach if the label specifies
At the same time as antibiotics (but 2-3 hours apart from the antibiotic dose)
Continue for 2-4 weeks after antibiotics to restore microbiome balance

Storage: some probiotics require refrigeration (especially S. boulardii and some multi-strain products). Shelf-stable formulations use desiccant packaging and freeze-drying — these are fine at room temperature. Read the label.

Probiotics for specific goals

IBS bloating & abdominal pain: B. infantis 35624, L. plantarum 299v, multi-strain products with bifidobacteria
Antibiotic-associated diarrhoea: S. boulardii (alongside and 2 weeks after antibiotics), L. rhamnosus GG
Traveler's diarrhoea prevention: S. boulardii, starting 5 days before travel
Constipation: B. lactis HN019, multi-strain products
Immune support in winter: L. rhamnosus GG, L. acidophilus NCFM, multi-strain
Women's vaginal health: L. rhamnosus GR-1 + L. reuteri RC-14 (look for women's-specific blends)

Top UK products

NOW Foods Clinical GI Probiotic — 50 billion CFU, 30 caps. Best value.
Life Extension FLORASSIST Probiotic Heart Health — 50 billion CFU, targeted formulation.
NOW Foods Saccharomyces boulardii 5 Billion — 60 caps, ideal alongside antibiotics.
California Gold Nutrition LactoBif 30 — 30 billion CFU, 5 strains, value tier.
Natural Factors Probiotic 12-12 — 12 strains, 12 billion CFU.

Frequently asked questions

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Probiotics UK Guide 2026: Strains, CFU, Top Products