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Oral Probiotics: An Introduction 

Probiotics are live microorganisms (e.g., bacteria) that are either the 

same as or similar to microorganisms found naturally in the human 

body and may be beneficial to health. Also referred to as “good 

bacteria” or “helpful bacteria,” probiotics are available to consumers 

in oral products such as dietary supplements and yogurts, as well as 

other products such as suppositories and creams. The U.S. Food and 

Drug Administration (FDA) has not approved any health claims for 

probiotics. This fact sheet provides a general overview of probiotics, 

with an emphasis on oral products, and suggests sources for 

additional information. 

© iStockphoto.com/humonia

Key Points 

Probiotic products are widely marketed, and consumer interest 

in probiotics is growing rapidly. Although some probiotic 

formulations have shown promise in research, strong scientific 

evidence to support specific uses of probiotics for most 

conditions is lacking. 

Probiotics have potential applications in many areas of human 

health, and research to gather scientific evidence about whether 

and how they work is moving forward. Additional clinical 

studies are needed to investigate the safety and efficacy of 

probiotics for specific uses. 

If you are thinking about using a probiotic dietary supplement, 

consult your health care provider first. Probiotics—like any form 

of complementary medicine—should not be used in place of 

conventional medical care or to delay seeking care if you are 

experiencing symptoms that concern you. 

Tell all your health care providers about any complementary 

approaches you use. Give them a full picture of what you do to 

manage your health. This will help ensure coordinated and safe care. 
Background 

The concept behind probiotics was introduced in the early 20th century, when Nobel laureate 

Elie Metchnikoff, known as the “father of probiotics,” proposed in The Prolongation of Life: 

Optimistic Studies that ingesting microorganisms could have substantial health benefits for 

humans. Microorganisms are invisible to the naked eye and exist virtually everywhere. 

Scientists continued to investigate the concept, and the term “probiotics”—meaning “for life”— 

eventually came into use. 

Picturing the human body as a “host” for bacteria and other microorganisms is helpful in 

understanding probiotics. The body, especially the lower gastrointestinal tract (the gut), 

contains a complex and diverse community of bacteria. (In the body of a healthy adult, cells of 

microorganisms are estimated to outnumber human cells by a factor of ten to one.) Although we 

tend to think of bacteria as harmful “germs,” many bacteria actually help the body function 

properly. Most probiotics are bacteria similar to the beneficial bacteria found naturally in the 

human gut. 

Various mechanisms may account for the effects of probiotics on human health. Possible 

mechanisms include altering the intestinal “microecology” (e.g., reducing harmful organisms in 

the intestine), producing antimicrobial compounds (substances that destroy or suppress the 

growth of microorganisms), and stimulating the body’s immune response. 

Probiotics commonly used in the United States include Lactobacillus and Bifidobacterium. There 

are many specific types of bacteria within each of these two broad groups, and health benefits 

associated with one type may not hold true for others. 

Probiotics, Prebiotics, and Synbiotics 

Probiotics are not the same as prebiotics—nondigestible substances that stimulate the growth 

and/or activity of potentially beneficial microorganisms. The term “synbiotics” refers to 

products that combine probiotics and prebiotics. 

Use of Probiotics in the United States 

In the United States, probiotics are available as dietary supplements (including capsules, tablets, 

and powders) and in dairy foods (such as yogurts with live active cultures). According to the 

2007 National Health Interview Survey, which included questions on Americans’ use of natural 

products other than vitamins and minerals, “prebiotics/probiotics” ranked fifth among natural 

products used for children, but were not among the top-ranking products for adults. Although 

probiotic products are more popular in Europe and Japan than in the United States, the U.S. 

consumer market for probiotics is growing rapidly. 

Although the FDA has not approved any health claims for probiotics, they are used for a variety of 

gastrointestinal conditions such as infectious diarrhea, diarrhea associated with using antibiotics, 

irritable bowel syndrome, and inflammatory bowel disease (e.g., ulcerative colitis and Crohn’s 

disease). Probiotics are also being used for preventing tooth decay and for preventing or treating 

other oral health problems such as gingivitis and periodontitis. Some—but not all—probiotic 

formulations have been widely studied and show considerable promise. However, the rapid 

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growth in marketing and consumer interest and use has outpaced scientific research on the safety 

and efficacy of probiotics for specific health applications. 

Government Regulation of Probiotics 

Government regulation of probiotics is complex. Depending on a probiotic product’s intended 

use, the FDA might regulate it as a dietary supplement, a food ingredient, or a drug. Many 

probiotic products are sold as dietary supplements, which do not require FDA approval prior to 

marketing. Dietary supplement labels may make claims about how the product affects the 

structure or function of the body without prior FDA approval, but they cannot make health 

claims (claims that the product reduces the risk of a disease) without the FDA’s consent. (For 

more information about dietary supplements, see Using Dietary Supplements Wisely at 

nccam.nih.gov/health/supplements/wiseuse.htm.) A product that is marketed as a drug must 

meet more stringent requirements. It must be proven safe and effective for its intended use 

through clinical studies (tests in people) and be approved by the FDA before it can be marketed. 

Status of Probiotics Research 

The potential of probiotics to benefit human health in many different ways has stimulated great 

interest and activity among researchers. For example, the National Center for Complementary 

and Alternative Medicine (NCCAM) is part of the National Institutes of Health (NIH) Probiotic and 

Prebiotic Working Group, a trans-NIH effort to identify gaps and challenges in prebiotic/probiotic 

research. 

Probiotic research is moving forward on two fronts: basic science (laboratory studies) and clinical 

trials to evaluate the safety and efficacy of probiotics for various medical conditions. Many early 

clinical trials of probiotics have had methodological limitations, and definitive clinical evidence to 

support using specific probiotic strains for specific health purposes is generally lacking. 

Nevertheless, there is preliminary evidence for several uses of probiotics, and more studies are 

under way. In particular, a recent review of the scientific evidence on the effectiveness of 

probiotics in acute infectious diarrhea concluded that there was evidence that probiotics can 

shorten the duration of diarrhea and reduce stool frequency but that more research was needed to 

establish exactly which probiotics should be used for which groups of people. 

In 2008, the journal Clinical Infectious Diseases published a special issue on probiotics, which 

included an overview of clinical applications. Based on a review of selected studies, the authors 

classified several applications according to the strength of evidence supporting the efficacy of 

probiotics in prevention and/or treatment. For example, the authors concluded that strong 

evidence exists for acute diarrhea and antibiotic-associated diarrhea, and substantial evidence 

exists for atopic eczema (a skin condition most commonly seen in infants). Promising 

applications include childhood respiratory infections, tooth decay, nasal pathogens (bacteria 

harbored in the nose), gastroenteritis relapses caused by Clostridium difficile bacteria after 

antibiotic therapy, and inflammatory bowel disease. The authors also discussed various 

potential future applications. 

Studies also indicate that probiotics may reduce side effects associated with treatment for 

Helicobacter pylori infection, the cause of most stomach ulcers. A systematic review suggests that 

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there is strong evidence that probiotics may reduce the risk of necrotizing enterocolitis, a severe 

intestinal condition of premature newborns. Other potential future applications include use in 

reducing cholesterol levels, treating obesity, and managing irritable bowel syndrome. 

Safety and Side Effects 

It appears that most people can use probiotics without experiencing any side effects—or with 

only mild gastrointestinal side effects such as gas—but there have been some case reports of 

serious adverse effects, and research on safety is ongoing. A 2008 review of probiotics safety 

noted that Lactobacillus rhamnosus GG has been widely studied in clinical trials for a variety of 

conditions and generally found to be safe. Nevertheless, a recent review of Lactobacillus and 

Bifidobacterium biology noted that long-term, cumulative effects of probiotics use, especially in 

children, are unknown, and also pointed to evidence that probiotics should not be used in 

critically ill patients. Similarly, a 2011 Agency for Healthcare Research and Quality assessment 

of the safety of probiotics, partly funded by NCCAM, concluded that the current evidence does 

not suggest a widespread risk of negative side effects associated with probiotics. However, the 

data on safety, particularly long-term safety, are limited, and the risk of serious side effects may 

be greater in people who have underlying health conditions. 

Concerns have also been raised about the quality of probiotic products. Some products have been 

found to contain smaller numbers of live microorganisms than expected. In addition, some 

products have been found to contain bacterial strains other than those listed as ingredients. 

If You Are Thinking About Using Probiotics 

Our understanding of probiotics is a work in progress. Although probiotic products are 

marketed for many different uses, scientific evidence supporting specific uses is still limited, 

and the FDA has not approved any health claims for probiotics. Before using probiotics, learn 

as much as you can by talking to your health care provider and researching reliable sources 

of information. 

Different probiotic products may contain different types of probiotic bacteria. Different types 

of probiotic bacteria may have different effects in the human body, and effects also may 

vary from person to person. 

Probiotics—or any form of complementary medicine—should not be used in place of 

conventional medical care or to delay seeking care if you are experiencing symptoms that 

concern you. If you are pregnant or nursing or are planning to give probiotics to a child, 

consulting your (or your child’s) health care provider is especially important. Anyone with a 

serious underlying health problem should be monitored closely for potential negative side 

effects while taking probiotics. 

Tell all your health care providers about any complementary and alternative approaches you 

use. Give them a full picture of what you do to manage your health. This will help ensure 

coordinated and safe care. For tips on talking with your health care providers about 

complementary and alternative medicine, see NCCAM’s Time to Talk campaign at 

nccam.nih.gov/timetotalk/. 

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NCCAM-Funded Research on Probiotics 

Recent NCCAM-supported research on probiotics has included clinical studies1 focused on: 

Prevention and treatment of diarrhea in infants 

Potential benefits for adults and children with irritable bowel syndrome and for people with 

minimal hepatic encephalopathy (a complication of liver disease) 

Treatment of an antibiotic-resistant type of bacteria 

Yogurt beverages as a way of giving high doses of probiotics to young children. 

NCCAM also supports laboratory studies that explore possible mechanisms of action for 

probiotics, providing a foundation for clinical research. For example, recent studies have found 

evidence that a strain of Lactobacillus reuteri might slow the growth of certain tumors, and that 

Lactobacillus acidophilus might enhance the effects of a vaccine against rotavirus infection—the 

most common cause of infectious diarrhea in infants and children worldwide. 

NCCAM’s clinical research program has designated probiotics as a high-priority topic for 

upcoming projects. Studies will focus on probiotics for addressing gastrointestinal disorders in 

infants and children, including necrotizing enterocolitis, colic, and irritable bowel syndrome; 

treating and preventing antibiotic-induced diarrhea; and enhancing the effects of flu vaccine. 

Selected References 

AlFaleh KM, Bassler D. Probiotics for prevention of necrotizing enterocolitis in preterm infants. Cochrane Database of 

Systematic Reviews. 2008;(1):CD005496. Accessed at http://www.thecochranelibrary.com on February 15, 2011. 

Allen SJ, Martinez EG, Gregorio GV, et al. Probiotics for treating acute infectious diarrhoea. Cochrane Database of Systematic 

Reviews. 2010;(11):CD003048. Accessed at http://www.thecochranelibrary.com on February 15, 2011. 

American Academy of Microbiology. Probiotic Microbes: The Scientific Basis. Report from a colloquium held in Baltimore, 

MD, November 5-7, 2005. Washington, DC: American Academy of Microbiology; 2006. 

Bonifait L, Chandad F, Grenier D. Probiotics for oral health: myth or reality? Journal (Canadian Dental Association). 

2009;75(8):585-590. 

Drisko J, Bischoff B, Giles C, et al. Evaluation of five probiotic products for label claims by DNA extraction and 

polymerase chain reaction analysis. Digestive Diseases and Sciences. 2005;50(6):1113-1117. 

Duffy LC, Sporn S, Hibberd P, et al. Lactobacilli and Bifidobacteria. In: Coates PM, Betz JM, Blackman MR, et al., eds. 

Encyclopedia of Dietary Supplements. 2nd ed. New York, NY: Informa Healthcare; 2010:469-478. 

1 NCCAM-supported clinical research includes studies conducted under FDA-approved investigational new drug 

applications. Before these studies can proceed to medically vulnerable populations, researchers carry out rigorous trials 

to determine safety in healthy adults or people with mild medical conditions. 

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Food and Agriculture Organization (FAO) of the United Nations and World Health Organization (WHO). Guidelines 

for the Evaluation of Probiotics in Food. Report of a Joint FAO/WHO Working Group on Drafting Guidelines for 

the Evaluation of Probiotics in Food, London, Ontario, Canada, April 30-May 1, 2002. Accessed at 

ftp://ftp.fao.org/es/esn/food/wgreport2.pdf on November 4, 2011. 

Goldin BR, Gorbach SL. Clinical indications for probiotics: an overview. Clinical Infectious Diseases. 2008;46(suppl 2):S96-S100. 

Hempel S, Newberry S, Ruelaz A, et al. Safety of Probiotics to Reduce Risk and Prevent or Treat Disease. Evidence 

Report/Technology Assessment no. 200. Agency for Healthcare Research and Quality Web site. Accessed at 

http://www.ahrq.gov/clinic/tp/probiotictp.htm on May 10, 2011. 

Hibberd PL, Hoffman FA, Heimbach JT, eds. Developing probiotics as food and drugs: scientific and regulatory 

challenges. Clinical Infectious Diseases. 2008;46(suppl 2). 

Hoffman FA, Heimbach JT, Sanders ME, et al. Executive summary: scientific and regulatory challenges of development 

of probiotics as foods and drugs. Clinical Infectious Diseases. 2008;46(suppl 2):S53-S57. 

Iyer C, Kosters A, Sethi G, et al. Probiotic Lactobacillus reuteri promotes TNF-induced apoptosis in human myeloid 

leukemia-derived cells by modulation of NF-kB and MAPK signaling. Cellular Microbiology. 2008;10(7):1442-1452. 

Kligler B, Cohrssen A. Probiotics. American Family Physician. 2008;78(9):1073-1078. 

McDade-Ngutter C, Versalovic J, Alexander W, et al. National Institutes of Health Gastrointestinal Microbiota and 

Advances in Prebiotic and Probiotic Research conference summary. Gastroenterology. 2009;136(5):1473-1475. 

Neish AS. Microbes in gastrointestinal health and disease. Gastroenterology. 2009;136(1):65-80. 

Petrof EO. Probiotics and gastrointestinal disease: clinical evidence and basic science. Anti-Inflammatory and Anti-Allergy 

Agents in Medicinal Chemistry. 2009;8(3):260-269. 

Preidis GA, Versalovic J. Targeting the human microbiome with antibiotics, probiotics, and prebiotics: gastroenterology 

enters the metagenomics era. Gastroenterology. 2009;136(6):2015-2031. 

Sethi T. Probiotics in pediatric care. Explore. 2009;5(4):245-249. 

Sharp RR, Achkar JP, Brinich MA, et al. Helping patients make informed choices about probiotics: a need for research. 

American Journal of Gastroenterology. 2009;104(4):809-813. 

Snydman DR. The safety of probiotics. Clinical Infectious Diseases. 2008;46(suppl 2):S104-S111. 

Tong JL, Ran ZH, Shen J, et al. Meta-analysis: the effect of supplementation with probiotics on eradication rates and 

adverse events during Helicobacter pylori eradication therapy. Alimentary Pharmacology and Therapeutics. 

2007;25(2):155-168. 

Vanderhoof JA, Young R. Probiotics in the United States. Clinical Infectious Diseases. 2008;46(suppl 2):S67-S72. 

Zhang W, Azevedo MSP, Wen K, et al. Probiotic Lactobacillus acidophilus enhances the immunogenicity of an oral 

rotavirus vaccine in gnotobiotic pigs. Vaccine. 2008;26(29-30):3655-3661. 

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Acknowledgments 

NCCAM thanks the following people for their technical expertise and review of the content 

update of this publication: Patricia Hibberd, M.D., Ph.D., Massachusetts General Hospital for 

Children; Marguerite Klein, M.S., NIH Office of Dietary Supplements; and Linda Duffy, Ph.D., 

and Jack Killen, M.D., NCCAM. 

This publication is not copyrighted and is in the public domain. 


Duplication is encouraged. 


NCCAM has provided this material for your information. It is not intended to substitute 

for the medical expertise and advice of your primary health care provider. We encourage 

you to discuss any decisions about treatment or care with your health care provider. The 

mention of any product, service, or therapy is not an endorsement by NCCAM. 

National Institutes of Health 

U.S. Department of Health and Human Services 

7 D345 

Created January 2007 

Updated November 2011