How to Choose a Probiotic: 7 Things to Check on the Label

By Natasha Trenev, Co-founder of Natren · Author & probiotic educator · Updated November 12, 2026 · Sources checked November 12, 2026

About the author: Natasha Trenev co-founded Natren with her husband, Yordan, in 1982, after growing up in her family's cultured-foods business, and has spent her career cultivating, formulating and explaining probiotic cultures. She is the author of Probiotics: Nature's Internal Healers (Avery, 1998), and her focus has always been education: helping people understand what is on a probiotic label and why it matters. Read her story.

If you're working out how to choose a probiotic, the front of the bottle won't tell you much. The useful information is in the small print: which strains are inside, how many live cultures are promised and until when, how the product should be stored, and what else is in the capsule or powder.

The short answer: To choose a probiotic, start with the strain, not the brand. Look for the full genus, species and strain on the label, a CFU count guaranteed through the expiration date, storage directions you can follow, and a format and allergen profile that fit your routine.

Natren has made probiotics since 1982, and we make our human probiotics in our own California facility. This guide uses our own labels as worked examples, but the seven checks work on any brand, including ours:

1. Find the full strain name
2. Match the strain to evidence
3. Check the CFU count and when it applies
4. Look at storage and shipping
5. Decide on single or multi-strain
6. Pick a format you'll take
7. Check allergens

Do you need a probiotic at all? (Do I need a probiotic?)

Not everyone does, and it's a fair question to ask before you compare labels. Probiotics are live microorganisms that, in adequate amounts, provide a health benefit. You can get live cultures from foods such as yogurt and kefir with live and active cultures, and from some fermented foods. Not every fermented food contains live probiotic microbes, though: baking, pasteurizing or filtering after fermentation can remove them (ISAPP).

A supplement may make sense if you want a specific, identified strain at a stated amount, or a dairy-free or vegan option that foods can't easily give you. It isn't a substitute for a varied diet or for seeing a clinician about symptoms. The National Center for Complementary and Integrative Health advises against using a probiotic as a reason to put off seeing your health care provider (NCCIH).

Talk to a clinician before starting a probiotic if you or the person you care for:

• has a weakened immune system or a serious underlying illness
• is critically ill or in hospital
• is a premature infant. The FDA has warned about serious, potentially fatal infections in preterm infants given products containing live microbes in hospital settings (FDA, 2023)
• is pregnant, breastfeeding, or taking prescription medicines

In healthy people, probiotics may cause minor effects such as gas, but they aren't risk-free for everyone (NIH Office of Dietary Supplements).

1. Find the full strain name, not just the species

What is a probiotic strain? A strain is a specific, identified line of a microbial species. It is written as three parts: the genus (for example Lactobacillus), the species (acidophilus) and a strain designation, the letters or numbers that follow (NAS).

The first rule of how to choose a probiotic is to read the strain, not the category. Two products can both say "Lactobacillus acidophilus" and contain completely different strains. Research is generally done on specific strains, and a result seen with one strain doesn't automatically apply to another, even within the same species (NCCIH; ISAPP).

Be cautious with labels that list only genus and species, or that group cultures under a "proprietary blend" with no strain designations and no amount per strain. You can't look up evidence for a strain the label doesn't name.

How to read a strain designation

Here are the three strains in Natren's Healthy Trinity, broken down the same way:

The 90-count bottle contains 25 billion CFU of B. bifidum Malyoth per capsule, for 35 billion CFU in total.

You may also see different names for the same culture. In 2020, scientists split the Lactobacillus genus into several new genera (for example, Lactobacillus rhamnosus became Lacticaseibacillus rhamnosus). L. acidophilus kept its name, and L. bulgaricus is formally written Lactobacillus delbrueckii subsp. bulgaricus, so labels and studies may use either the older or the newer name. The strain designation is what stays constant, so search for it when you look up research.

For a plain-English profile of each Natren culture, see our probiotic strain guide.

2. Match the strain to evidence, not marketing (clinically studied probiotic research)

Once you know the strain, ask a narrower question: has this strain been studied, in people like you, at roughly this amount? ISAPP, the International Scientific Association for Probiotics and Prebiotics, recommends choosing products with evidence behind them rather than assuming every probiotic works the same way (ISAPP).

How to check:

• Search the strain designation, not just the species, in PubMed or ClinicalTrials.gov.
• Look at who was studied. Results in hospitalized adults may not apply to a healthy child, and the reverse.
• Check the amount and product. A study may have used a different dose or formulation from the one on the shelf.
• Read the limits. Small or open-label studies are a starting point, not proof. A registered trial with no posted results tells you a study happened, not what it found.

"Clinically studied" on a label can mean many things: the exact product was tested, an ingredient was tested in a different form, or the strain appears in any published paper at all. Ask the brand which study, which formula and which outcome.

We try to hold ourselves to the same standard. Our research behind our cultures page summarizes each study's design, population and limits, links to the primary source, and notes where results were null or not posted.

3. Check the CFU count and when it applies (probiotic CFU)

What does CFU mean on a probiotic? CFU stands for colony-forming units, an estimate of how many live, viable microbes are in a serving. Labels usually show it in billions, for example "1 billion CFU" (NIH ODS).

Live cultures decline over time, so the most important question isn't how big the number is but when it applies. You'll see two kinds of wording:

• "At time of manufacture" describes the bottle on the day it was made. It says nothing about what's left by the time you open it, or by the last dose before expiry.
• "Through expiration" (or "at end of shelf life") is a minimum the brand stands behind up to the date on the bottle, provided you store it as directed.

The NIH Office of Dietary Supplements advises looking for the CFU count at the end of the product's shelf life, not at manufacture (NIH ODS). ISAPP gives the same advice (ISAPP).

On a Natren label, Healthy Trinity's minimum counts are guaranteed through expiration when kept dry and refrigerated, and the label says not to freeze it: 30 billion CFU per capsule in the 30- and 60-count bottles, and 35 billion CFU per capsule in the 90-count.

You may also see a weight (in milligrams) in the Supplement Facts panel. FDA rules require a weight, and FDA draft guidance lets brands add a CFU count next to it (FDA). The CFU figure is the one that tells you about live cultures.

Is a higher CFU count better?

Not by itself. A higher CFU count doesn't necessarily mean a product will do more for you (NIH ODS), and there is no single dose that suits every strain or person. The useful comparison is the amount studied for that strain, the amount guaranteed through expiration, and the directions on the label.

4. Look at storage and how it's shipped

Probiotics are alive, and heat, moisture, air and time all reduce the number of viable cultures. That's why the storage line on the label matters as much as the CFU claim: a potency guarantee only holds if the product is kept the way the label says.

Refrigerated vs shelf-stable probiotics

Some probiotics need refrigeration and others are formulated to be stored at room temperature (NIH ODS; ISAPP). Neither is automatically better. What matters is that:

• the label gives clear storage directions you can follow at home, at work and when you travel
• potency is guaranteed through expiration under those conditions
• the product was stored correctly before it reached you

What to check when you buy

• In a store: if the label says "keep refrigerated", the product should be in a refrigerated case.
• Online: check whether refrigerated products are shipped with insulation or cold packs, and avoid long transit in hot weather where you can.
• At home: put refrigerated products back in the fridge as soon as they arrive, keep the lid closed, and keep them dry.

Natren ships its probiotics in thermal packaging. Healthy Trinity's minimum count is guaranteed through expiration when it's kept dry and refrigerated, and its label says not to freeze it; for any other product, check the storage directions on its label. Learn why we refrigerate our probiotics, or read do probiotics need to be refrigerated?

5. Single strain or multi-strain?

More strains don't automatically mean more benefit. Strains can behave differently alone than in combination, and evidence for a blend applies to that blend at the studied amounts, not to each strain added to it. A long ingredient list can also mean a small amount of each strain.

What the evidence does support is narrower: look for every strain to be identified by its full designation, with an amount per strain, and for some research on that strain or combination. A single-strain product makes it easy to know exactly what you're taking. A multi-strain product can make sense when the specific combination has been studied or is formulated deliberately.

Natren makes both. Megadophilus, Bifido Factor and Digesta-Lac each contain one strain. Healthy Trinity combines three named strains in one oil-based capsule. For more on how strains interact, read the multi-strain problem.

6. Pick a format you'll actually take (probiotic capsules vs powder)

The best format is the one that fits your routine and storage habits, and that you'll take as directed.

Probiotics for children and infants

Children need age-appropriate products and amounts, and powders are often easier to give. Check minimum ages on chewables, and speak to your pediatrician before starting a probiotic, especially for an infant. Never give a probiotic to a premature infant without medical direction. Life Start is a Bifidobacterium infantis NLS powder that contains milk. Life Start Vegan is dairy-free, with 1 billion CFU per 1 g serving, and Life Start 2 uses a goat-milk formula in powder and capsules. Check each product's label and product page for age guidance and directions. See probiotics for kids by age and format and B. infantis for babies.

Probiotics for pets

Give pets a product formulated and labelled for their species rather than a human supplement, and check with your veterinarian. Caninedophilus (dogs) and Felinedophilus (cats) are gels containing L. acidophilus NAS and Enterococcus faecium NCIMB 10415, 6 billion CFU per 2 g serving. Gastro Vegi-Dophilus is a dairy-free pet powder with L. acidophilus DDS-1 and L. bulgaricus LB-51. See Natren for pets.

7. Check allergens: dairy, dairy-free or vegan

Dairy can turn up in a probiotic in two ways: the medium the cultures are grown in, and the finished product's other ingredients. Capsules may also be made from gelatin, which matters if you avoid animal products.

To check any label:

• read the "Other ingredients" line under the Supplement Facts panel
• read the allergen statement (for example, "Contains: milk")
• look for a clear dairy-free or vegan statement if you need one, and ask the brand what the cultures are grown on if it isn't stated

Natren's Megadophilus comes in dairy capsules, dairy-free capsules, dairy powder and vegan powder, and Bifido Factor comes in dairy powder, vegan powder and capsules. Life Start Vegan is dairy-free. Healthy Trinity's capsules are made with sunflower oil, gelatin and mixed tocopherols. For the full allergen statement on any product, check its label or product page. Browse dairy-free probiotics, or read our guide to vegan and dairy-free probiotics.

Your probiotic label checklist

Use these checks on any probiotic, in the store or online:

1. Strain: every culture is named by genus, species and strain designation.
2. Evidence: you can find research on that strain, in people like you, at a similar amount.
3. CFU: the count is guaranteed through expiration, not only at manufacture.
4. Storage: the directions are clear and you can follow them; it was stored correctly before you bought it.
5. Strain count: every strain in a blend has its own amount listed.
6. Format: it suits your routine, and any minimum age or use directions fit.
7. Allergens: other ingredients and the allergen statement fit your diet.
8. Manufacturer: the label gives the company's name, address and a way to contact it to ask questions or report a problem.

Questions to ask any probiotic brand

• What are the full strain designations in this product, and how much of each strain is in a serving?
• Is the CFU count guaranteed through the expiration date, and under what storage conditions?
• Who manufactures the product, and where?
• How is the product stored before it ships, and how is it packed for transit?
• What are the cultures grown on, and what allergens are in the finished product?
• Which studies used this strain or this formula, and at what amount?
• How do I report a problem or a side effect? (You can also report problems with supplements to the FDA.)

Frequently asked questions

How long should I take a probiotic before deciding?

Responses vary from person to person. ISAPP suggests trying a product consistently for about a month to see whether it suits you (ISAPP). Follow the label directions, and talk to your health care provider if you have ongoing symptoms.

Should I take probiotics with food?

Follow the directions on your product's label, since they're written for that formula. Taking it at the same time each day can make it easier to remember.

Can I take a probiotic with antibiotics?

Ask the doctor or pharmacist who prescribed the antibiotic before combining them. If they agree, follow their advice on how to time the two. A probiotic isn't a substitute for any medicine you've been prescribed.

How can I tell whether a probiotic contains dairy?

Check the "Other ingredients" line and the allergen statement on the label. If the product doesn't say whether the cultures are grown on a dairy medium, ask the manufacturer.

Where Natren's formulas fit

If you've worked through the checklist and want to compare our products, here's how they line up by need and format:

Browse all Natren probiotics, and check each product page for its full label. Questions about a Natren product? Call customer service at 1-866-462-8736 or email customerservice@natren.com.

These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease.

The bottom line

Knowing how to choose a probiotic comes down to reading the label: a named strain, evidence for that strain, a CFU count guaranteed through expiration, storage you can follow, and a format and ingredient list that fit your life. Before you start any probiotic, talk to your health care provider, especially if you're pregnant, take medication or have a health condition.

Sources

All URLs checked November 12, 2026.

1. National Institutes of Health, Office of Dietary Supplements. Probiotics: Fact Sheet for Consumers. https://ods.od.nih.gov/factsheets/Probiotics-Consumer/
2. National Center for Complementary and Integrative Health. Probiotics: Usefulness and Safety. Last updated August 2019. https://www.nccih.nih.gov/health/probiotics-what-you-need-to-know
3. International Scientific Association for Probiotics and Prebiotics (ISAPP). How to choose a probiotic. Updated September 5, 2025. https://isappscience.org/resource/how-to-choose-a-probiotic/
4. ISAPP. Do all fermented foods contain a probiotic? https://isappscience.org/resource/do-all-fermented-foods-contain-a-probiotic/
5. U.S. Food and Drug Administration. FDA Raises Concerns About Probiotic Products Sold for Use in Hospitalized Preterm Infants. October 26, 2023. https://www.fda.gov/news-events/press-announcements/fda-raises-concerns-about-probiotic-products-sold-use-hospitalized-preterm-infants
6. FDA. Draft Guidance for Industry: Policy Regarding Quantitative Labeling of Dietary Supplements Containing Live Microbials. September 2018. https://www.fda.gov/regulatory-information/search-fda-guidance-documents/draft-guidance-industry-policy-regarding-quantitative-labeling-dietary-supplements-containing-live
7. FDA. Dietary Supplement Labeling Guide. https://www.fda.gov/food/dietary-supplements-guidance-documents-regulatory-information/dietary-supplement-labeling-guide
8. FDA. Questions and Answers on Dietary Supplements. Content current as of August 27, 2026. https://www.fda.gov/food/information-consumers-using-dietary-supplements/questions-and-answers-dietary-supplements
9. FDA. How to Report a Problem with Dietary Supplements. https://www.fda.gov/food/dietary-supplements/how-report-problem-dietary-supplements
10. Natren. The research behind our cultures (study summaries with links to PubMed and ClinicalTrials.gov records). https://www.natren.com/pages/natren-science