Probiotics for Beginners: What the Evidence Shows

Quick answer

Probiotics for beginners, in short: Probiotics are live “friendly” bacteria or yeasts sold in capsules, powders and drinks. The best evidence is for people taking antibiotics: across 42 trials, those who also took certain probiotics had less diarrhea [1]. For irritable bowel syndrome (IBS), some products helped some people, but the evidence is mostly low quality [2]. For healthy people looking for general benefits, the evidence is thin [3]. Which strain you take matters a lot. We rate the evidence B: useful for a specific outcome, with big gaps elsewhere.

What is probiotics?

The scientific definition of a probiotic is “live microorganisms which, when administered in adequate amounts, confer a health benefit on the host” [4]. That wording matters: a product only counts if the specific strain has been shown to help. Yogurt that merely contains live cultures doesn’t automatically qualify.

Most supplements use bacteria from the Lactobacillus and Bifidobacterium families, or a yeast called Saccharomyces. Different strains can behave very differently, so “probiotics” is really many different products rather than one thing.

Probiotics for beginners: what might they help with?

Possible benefit	Rating	In plain words
Diarrhea while taking antibiotics (adults)	Strong	Lower risk in a large review, but only for certain strains and where risk is moderate or high [1]
IBS symptoms	Promising	Some strains helped, but certainty was low to very low for most [2]
Weight, waist size in healthy adults	Early	Tiny improvements, in poor-quality trials [3]
General “gut health” or immunity in healthy people	Early	Experts say there are many unknowns and conflicting results [5]

Ratings describe how good the research is, not a promise that it will work for you.

What the research says

• Antibiotics (42 trials, 11,305 adults). Taking a probiotic alongside antibiotics reduced the risk of antibiotic-associated diarrhea by 37% (risk ratio 0.63). The overall certainty was moderate. Only certain strains, mainly Lactobacillus and Bifidobacterium, worked. A higher dose beat a lower dose of the same product. In studies where people had a low risk of diarrhea to begin with, there was no difference [1]. PubMed · DOI
• IBS (82 trials, 10,332 adults). Some probiotics, including certain Escherichia, Lactobacillus, Bifidobacterium and combination products, showed a benefit for some symptoms. But only 24 trials had a low risk of bias, and for almost all strains the certainty was low or very low. Probiotics did not cause more side effects than placebo [2]. PubMed · DOI
• Healthy people (61 trials, 5,422 adults). Probiotics gave very small improvements in BMI and waist size. The authors warned that poor trial quality makes firm conclusions hard [3]. PubMed · DOI
• Expert view. A 2019 Nature Medicine review described the field’s “many unknowns”: results conflict for many strains, and better-quality evidence and clearer product rules are needed [5]. PubMed · DOI

The big lesson: results for one strain can’t be assumed for another, and “probiotic” on a label doesn’t tell you which one helped in a study.

Amounts and how people take it

These are amounts used in studies, not recommendations.

• Dose: probiotic amounts are measured in “colony-forming units” (CFU). In the healthy-people review, daily doses ranged widely, from about a million to ten billion CFU [3]. In the antibiotics review, higher doses of the same product worked better than lower ones [1].
• Strain: look for the full strain name (genus, species and a code), because benefits are strain-specific [1][2].
• Timing: in the antibiotics review, probiotics were taken alongside the antibiotic course [1]. The sources we checked don’t give a firm rule on time of day.
• Form: capsules, powders, yogurts and drinks are all used. We found no verified source ranking one above another.

Side effects, interactions and who should check first

For most healthy people, probiotics are well tolerated. The IBS review found no higher rate of side effects than placebo [2].

However, a 2015 safety review noted that safety outcomes are inconsistently reported in trials, and that theoretical risks include infections that spread into the bloodstream and excessive immune stimulation in susceptible people [6]. Serious problems appear to be rare, but the research is not complete.

Who should check with a doctor or pharmacist first

Check with a doctor or pharmacist first if you:

• have a weakened immune system, are seriously ill or in hospital, or are on medicines that suppress immunity [6]
• are giving probiotics to a baby or young child
• are pregnant or breastfeeding
• are taking antibiotics and want to take probiotics alongside them (this is what the research studied, but ask what suits you)

Where to buy

Look for the active form and amount (the full strain name and the CFU count per serving), a stated third-party testing certificate you can check, and work out the price per daily dose rather than comparing pack prices.

FAQ

What are probiotics?

Probiotics are live “friendly” bacteria or yeasts sold in capsules, powders and drinks. The scientific definition is “live microorganisms which, when administered in adequate amounts, confer a health benefit on the host” [4]. A product only counts if its specific strain has been shown to help, so yogurt that merely contains live cultures doesn’t automatically qualify.

Do probiotics work?

The best evidence is for people taking antibiotics: across 42 trials, taking certain probiotics alongside antibiotics cut the risk of diarrhea by 37% [1]. For IBS some strains helped some people, but certainty was low or very low for most [2]. For healthy people the evidence is thin, with very small BMI and waist changes in poor-quality trials [3].

How much probiotics per day?

Amounts are measured in colony-forming units (CFU). In the healthy-people review, daily doses ranged from about a million to ten billion CFU [3], and in the antibiotics review a higher dose of the same product beat a lower one [1]. Benefits are strain-specific [1][2], so look for the full strain name. These are study amounts, not recommendations.

Who should not take probiotics?

Check with a doctor or pharmacist first if you have a weakened immune system, are seriously ill or in hospital, or take medicines that suppress immunity [6]. Also check first if you are giving probiotics to a baby or young child, or if you are pregnant or breastfeeding. A safety review noted theoretical risks such as infections spreading into the bloodstream in susceptible people [6].

Can you take probiotics with antibiotics?

That is what the best research studied: in the antibiotics review, probiotics were taken alongside the antibiotic course, and certain strains reduced diarrhea [1]. The sources we checked don’t give a rule on timing, so ask a doctor or pharmacist what suits you, especially if your immune system is weakened [6].

Related pages

• Inulin
• Berberine
• Collagen
• Longevity supplements for beginners: where this fits in a beginner’s routine
• All supplements A-Z

Talk to your doctor

This page is for general information and is not medical advice. Speak to a doctor or pharmacist before starting any supplement, especially if you are pregnant or breastfeeding, take any medicine, or have a health condition.

References

We cite only studies and official pages we checked against PubMed, the publisher or the agency’s own site. The A to E evidence grades are explained in our editorial policy. See also our medical disclaimer and affiliate disclosure.

1. Goodman C, Keating G, Georgousopoulou E, et al. Probiotics for the prevention of antibiotic-associated diarrhoea: a systematic review and meta-analysis. BMJ Open. 2021. PubMed · DOI
2. Goodoory VC, Khasawneh M, Black CJ, et al. Efficacy of Probiotics in Irritable Bowel Syndrome: Systematic Review and Meta-analysis. Gastroenterology. 2023. PubMed · DOI
3. Skonieczna-Żydecka K, Kaźmierczak-Siedlecka K, Kaczmarczyk M, et al. The Effect of Probiotics and Synbiotics on Risk Factors Associated with Cardiometabolic Diseases in Healthy People-A Systematic Review and Meta-Analysis with Meta-Regression of Randomized Controlled Trials. J Clin Med. 2020. PubMed · DOI
4. Hill C, Guarner F, Reid G, et al. Expert consensus document. The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic. Nat Rev Gastroenterol Hepatol. 2014. PubMed · DOI
5. Suez J, Zmora N, Segal E, et al. The pros, cons, and many unknowns of probiotics. Nat Med. 2019. PubMed · DOI
6. Doron S, Snydman DR. Risk and safety of probiotics. Clin Infect Dis. 2015. PubMed · DOI