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Probiotics: In Depth

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What's the Bottom Line?

How much do we know about probiotics?

Although a great deal of research has been done on probiotics, much remains to be learned.

What do we know about the usefulness of probiotics?

Some probiotics may help to prevent diarrhea that's caused by infections or antibiotics. They may also help with symptoms of irritable bowel syndrome. However, benefits have not been conclusively demonstrated, and not all probiotics have the same effects.

What do we know about the safety of probiotics?

In healthy people, probiotics usually have only minor side effects, if any. However, in people with underlying health problems (for example, weakened immune systems), serious complications such as infections have occasionally been reported.

What Are Probiotics?

Probiotics are live microorganisms that are intended to have health benefits. Products sold as probiotics include foods (such as yogurt), dietary supplements, and products that aren't used orally, such as skin creams.

Although people often think of bacteria and other microorganisms as harmful “germs,” many microorganisms help our bodies function properly. For example, bacteria that are normally present in our intestines help digest food, destroy disease-causing microorganisms, and produce vitamins. Large numbers of microorganisms live on and in our bodies. In fact, microorganisms in the human body outnumber human cells by 10 to 1. Many of the microorganisms in probiotic products are the same as or similar to microorganisms that naturally live in our bodies.

The History of Probiotics

What Kinds of Microorganisms Are In Probiotics?

Probiotics, Prebiotics, and Synbiotics

How Popular Are Probiotics?

What the Science Says About the Effectiveness of Probiotics

Researchers have studied probiotics to find out whether they might help prevent or treat a variety of health problems, including:

  • Digestive disorders such as diarrhea caused by infections, antibiotic-associated diarrhea, irritable bowel syndrome, and inflammatory bowel disease
  • Allergic disorders such as atopic dermatitis (eczema) and allergic rhinitis (hay fever)
  • Tooth decay, periodontal disease, and other oral health problems
  • Colic in infants
  • Liver disease
  • The common cold
  • Prevention of necrotizing enterocolitis in very low birth weight infants.

There’s preliminary evidence that some probiotics are helpful in preventing diarrhea caused by infections and antibiotics and in improving symptoms of irritable bowel syndrome, but more needs to be learned. We still don’t know which probiotics are helpful and which are not. We also don’t know how much of the probiotic people would have to take or who would most likely benefit from taking probiotics. Even for the conditions that have been studied the most, researchers are still working toward finding the answers to these questions.

Probiotics are not all alike. For example, if a specific kind of Lactobacillus helps prevent an illness, that doesn’t necessarily mean that another kind of Lactobacillus would have the same effect or that any of the Bifidobacterium probiotics would do the same thing.

Although some probiotics have shown promise in research studies, strong scientific evidence to support specific uses of probiotics for most health conditions is lacking. The U.S. Food and Drug Administration (FDA) has not approved any probiotics for preventing or treating any health problem. Some experts have cautioned that the rapid growth in marketing and use of probiotics may have outpaced scientific research for many of their proposed uses and benefits.

How Might Probiotics Work?

Government Regulation of Probiotics

What the Science Says About the Safety and Side Effects of Probiotics

Whether probiotics are likely to be safe for you depends on the state of your health.

  • In people who are generally healthy, probiotics have a good safety record. Side effects, if they occur at all, usually consist only of mild digestive symptoms such as gas.
  • On the other hand, there have been reports linking probiotics to severe side effects, such as dangerous infections, in people with serious underlying medical problems. The people who are most at risk of severe side effects include critically ill patients, those who have had surgery, very sick infants, and people with weakened immune systems

Even for healthy people, there are uncertainties about the safety of probiotics. Because many research studies on probiotics haven’t looked closely at safety, there isn’t enough information right now to answer some safety questions. Most of our knowledge about safety comes from studies of Lactobacillus and Bifidobacterium; less is known about other probiotics. Information on the long-term safety of probiotics is limited, and safety may differ from one type of probiotic to another. For example, even though a National Center for Complementary and Integrative Health (NCCIH)-funded study showed that a particular kind of Lactobacillus appears safe in healthy adults age 65 and older, this does not mean that all probiotics would necessarily be safe for people in this age group.

Quality Concerns About Probiotic Products

NCCIH-Funded Research

NCCIH is sponsoring a variety of research projects related to probiotics.

More information

More To Consider

  • Don’t replace scientifically proven treatments with unproven products and practices. Don’t use a complementary health product, such as probiotics, as a reason to postpone seeing your health care provider about any health problem.
  • If you’re considering a probiotic dietary supplement, consult your health care provider first. This is especially important if you have health problems. Anyone with a serious underlying health condition should be monitored closely while taking probiotics.
  • If you’re pregnant or nursing a child, or if you’re considering giving a child a dietary supplement, such as probiotics, it’s especially important to consult your (or your child’s) health care provider.
  • Tell all your health care providers about any complementary or integrative health 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 More Information

NCCIH Clearinghouse

The NCCIH Clearinghouse provides information on NCCIH and complementary and integrative health approaches, including publications and searches of Federal databases of scientific and medical literature. The Clearinghouse does not provide medical advice, treatment recommendations, or referrals to practitioners.

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PubMed®

A service of the National Library of Medicine, PubMed® contains publication information and (in most cases) brief summaries of articles from scientific and medical journals. For guidance from NCCIH on using PubMed, see How To Find Information About Complementary Health Approaches on PubMed.

MedlinePlus

To provide resources that help answer health questions, MedlinePlus (a service of the National Library of Medicine) brings together authoritative information from the National Institutes of Health as well as other Government agencies and health-related organizations.

Key References

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Additional References

Acknowledgments

NCCIH thanks Patricia Hibberd, M.D., Ph.D., Harvard Medical School and Linda Duffy, Ph.D., and David Shurtleff, Ph.D., NCCIH, for their contributions to the 2015 update of this publication.

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

NCCIH 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 NCCIH.

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NCCIH Pub No.: 
D345
Last Updated: 
October 2016

This page last modified January 16, 2017