What Should You Know About Probiotics?

Before investing in supplements, learn exactly how probiotics work

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Probiotics are live microorganisms, including bacteria and yeasts, found in some foods, supplements, and skin care products. They may have health benefits, but when, how, and who should use probiotics is not yet well understood.

The types (strains) of probiotics that may aid men’s health (such as for testosterone levels) or women’s health (such as for vaginal health) are also controversial.

This article will present some of the evidence for and against using probiotics to support various health conditions.

Person reading a bottle of probiotics at a pharmacy

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How Are Probiotics Good for You?

Probiotics are sold in many formulations and products. How they may benefit health is an active area of study, but there aren’t many conclusions available yet.

The human body has many different types of microorganisms that live on and inside it, called the microbiome. A probiotic supplement aims to change the makeup of the microbiome to provide some health benefits. The challenge is in knowing which probiotic is helpful and for which health problem.

There is little in the way of guidance available on who should take probiotics and when. However, people taking antibiotics, having a gastrointestinal infection, or having digestive symptoms (such as diarrhea or constipation) may want to talk to a healthcare provider about starting a probiotic.

Preventing Antibiotic-Associated Diarrhea

Some people may have diarrhea after taking antibiotics for an infection. This is because an antibiotic may kill the good bacteria of the gut microbiome along with the bacteria causing the infection. This results in dysbiosis, which is an imbalance in the gut microbiome. It’s not yet known exactly which probiotic might work best to prevent diarrhea after a course of antibiotics.

Preventing Clostridium difficile (C. diff) Infections

C. diff is a type of bacteria that can infect the digestive system and cause severe diarrhea and other complications. There has been some study into using probiotics to prevent these infections, but there is little information on which strains of bacteria would work best against it. It’s recommended that probiotics only be used in clinical trials for active C. diff infections.

After Helicobacter pylori (H. pylori) Treatment

H. pylori is a bacterium that can cause an infection in the stomach. Treatment includes antibiotics and other medications. Probiotics are being studied in preventing symptoms that may happen after H. pylori treatment. It’s not yet known which types of probiotics and in what dosage and combination might work best.

Preventing Necrotizing Enterocolitis

Babies born prematurely can develop necrotizing enterocolitis in their digestive system, which can be life-threatening. Probiotics are being studied to help prevent this condition. Because preterm infants are so fragile, a major concern is in the reliability and purity of probiotics on the market for this age group.

The American Gastroenterological Association (AGA) recommends certain probiotics that can be used in babies born before 37 weeks or in low birth weight babies (those weighing less than 5 pounds, 5 ounces).

Preventing Infections After Surgery

The microflora is the bacteria on the skin. Infections can develop at incision sites or elsewhere in the body after surgery. Probiotics may be used to try to prevent infections, but there’s not much evidence for their use.

Traveler’s Diarrhea

An infection causing diarrhea that occurs after consuming contaminated food or drink is referred to as traveler's diarrhea. Preventing this infection with probiotics has been the subject of a few studies. There is some evidence that a probiotic yeast, Saccharomyces boulardii, may help prevent traveler’s diarrhea, but it is not yet settled science.

Diarrhea in Children

Diarrhea in children is a major cause of disease in the developing world. Probiotics have been studied for this use and are recommended by some experts in Latin America. However, only certain types and probiotics that have been clinically tested are recommended.

The AGA recommends that probiotics not be used for diarrhea from gastroenteritis (“stomach flu") in children.

Inflammatory Bowel Disease (IBD)

The studies on probiotics to treat the two main forms of IBD (Crohn’s disease and ulcerative colitis) have found no benefit. The AGA does not recommend probiotic use in people with IBD.

For people who have had ileal pouch–anal anastomosis (IPAA) surgery (also called a j-pouch) for ulcerative colitis, a type of probiotic made up of several strains is sometimes recommended by healthcare providers. This combination of strains includes Lactobacillus paracasei subspecies (subsp.) paracasei, Lactobacillus plantarum, Lactobacillus acidophilus, Lactobacillus delbrueckii  subsp. bulgaricus, Bifidobacterium longum subsp. longum, Bifidobacterium breve, Bifidobacterium longum subsp. infantis, and Streptococcus salivarius subsp. thermophilus.

Irritable Bowel Syndrome (IBS)

Results of clinical trials on how probiotics may help with the symptoms of IBS have been mixed. Some show benefit, while others show no improvement. For that reason, probiotics aren’t currently recommended for IBS.

Testosterone Levels

It’s thought that some inflammatory conditions or other diseases and conditions can lead to reduced levels of testosterone (a sex hormone mainly made in the testicles). Most of the studies so far have been in mice, but at least one study showed that there may be a connection between the gut microbiome, the use of probiotics, and maintaining testosterone levels. There is no guidance on how to use probiotics for testosterone levels.

Vaginal Health

The vagina contains microorganisms that can become out of balance. This could lead to infections, such as bacterial vaginosis. There is no guidance on who might benefit from vaginal probiotics. One 2020 study has shown that Lactobacillus rhamnosus GR-1 and Lactobacillus reuteri RC-14 may help prevent or treat some cases of bacterial vaginosis.

Prebiotics vs. Probiotics

Prebiotics are different from probiotics. Prebiotics are plant fibers that aren’t digested by the gastrointestinal system. They are what probiotic organisms use for food. Both probiotics and prebiotics play a role in gut health.

When to Take Probiotics

It is generally thought in order to have an effect, probiotics should be taken at any time of day as long as they are taken daily for a certain period of time. The label on the probiotic supplement should give instructions on when and how to take it.

Probiotic Supplements

At least one study found that taking probiotics 30 minutes before a meal may help the live strains survive better in the digestive system. However, there have been other studies showing that taking probiotics with a meal or at a certain time of day do not have an effect.

One small 2017 study from Italy explored whether the time of day a probiotic is taken matters. The two strains studied were Bifidobacterium longum and Lactobacillus rhamnosus. One group of study participants took the supplement before breakfast and another group took it after breakfast. The strains showed up in the same amounts in both groups. This discounts the importance of the time of day that taking a probiotic is most effective.

Reading the label on the probiotic supplement is key to understanding when to take it. There should be a daily dosage listed. There should also be a suggestion about taking it on an empty stomach, with milk, or with a small meal or snack. Following this guidance is important because it is based on the type and strain of the probiotics.

Probiotic supplements are usually only taken for a specific amount of time—usually days or, at most, weeks. There isn’t any evidence that they are any more helpful if taken every day for long periods of time. They can be expensive, so it’s important to get advice from a healthcare provider on how long to take them.

Probiotic Foods

Probiotics are found in some foods, particularly fermented foods, which include:

  • Some types of cheese
  • Kefir (fermented milk drink)
  • Kimchi (fermented cabbage)
  • Kombucha (fermented tea)
  • Sauerkraut (fermented cabbage)
  • Miso (fermented soybean paste)
  • Raw unfiltered apple cider vinegar (from fermented apple sugars)
  • Some types of pickles
  • Yogurt

Some foods may have probiotics added to them. It is difficult to know the actual probiotic content of a food because the microorganisms are living, and some may die between the production of the food and when it is eaten.

In general, kefir and yogurt are the foods that have the highest amount of probiotic organisms in them. It’s important to look for the words “live cultures” on the label so that it’s clear the food contains microorganisms.

Considerations for Those With Celiac Disease

For people who live with celiac disease and must avoid gluten, probiotic choices can be tricky. One study showed that many probiotic supplements may contain gluten.

Possible Side Effects From Probiotics 

Probiotics are generally considered safe in people who are in good health. However, adverse effects from probiotics are possible. In addition, probiotics may not be safe for people who live with serious health conditions.

Probiotic use may be risky in infants, especially those born prematurely or with serious health conditions. People who are critically ill, immunocompromised, or those who have cancer may be at risk for harmful effects from probiotics.

Probiotics, in general, are not federally regulated because they are sold as dietary supplements and not drugs in the United States. For this reason, they may contain materials or strains that are unintended or not listed on the label. There is a risk of undesirable genetic materials in the probiotics transferring to the person receiving them.

Potential adverse effects of probiotics on the digestive system include:

  • Bloating
  • Constipation
  • Gas
  • Vomiting
  • Diarrhea
  • Nausea
  • Cramping

Rashes and acne have also been reported. In some people, these effects may lessen or go away if the probiotics are taken regularly.

Managing Side Effects

For lessening the digestive symptoms of probiotics, lowering the dose and then increasing it slowly may help. In addition, staying hydrated by drinking enough water may also be helpful in some cases.

Popular Forms of Probiotic Supplements 

Probiotics come in many forms. Those taken orally include chewable tablets, freeze-dried capsules, powders, or liquids. They may be found in drug, vitamin, and health food stores as a supplement but might also be included in foods.

Probiotic supplements may contain more than one strain of microorganisms. For most people, the list of bacterial strains on the label will not have much meaning. 

For this reason, the World Gastroenterology Organisation recommends that healthcare providers give people clear instructions on choosing a probiotic. The probiotic recommended should be based on evidence that it may be helpful for a particular condition. Trying a probiotic that hasn’t been shown to have an effect may not be useful.

Some of the common bacterial strains in probiotics include species of:

  • Bacillus
  • Bifidobacterium (including adolescentis, animalis, bifidum, breve, and longum)
  • Lactobacillus (including acidophilus, casei, fermentum, gasseri, johnsonii, paracasei, plantarum, rhamnosus, and salivarius)
  • Lactococcus
  • Pediococcus 
  • Propionibacterium 
  • Streptococcus 

Some of the common types of yeasts that are in probiotics are:

  • Saccharomyces cerevisiae
  • Saccharomyces carisbergensis
  • Saccharomyces boulardii 

Non-yeast fungi can also be considered probiotics, and common types include:

  • Aspergillus niger 
  • Aspergillus oryzae

Colony Forming Units

The label for a probiotic supplement should contain the number of colony forming units (CFU) in the product. A higher number does not always mean that the product is “better” or more effective.

What is important is the CFU when the product is used, because it is the “live” microorganisms that convey the health benefits. When products expire, according to the date on the label, they may not have as many live CFUs.


Probiotics are a multibillion dollar industry, yet there is still a need for quality evidence on their use. Probiotic supplements may be helpful for some diseases and conditions. People will need guidance from healthcare providers on which strains or formulations to use.

Instructions on taking a probiotic, including what time of day, with a meal or between meals, and for how many days, should be included on the supplement label.

15 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading

By Amber J. Tresca
Amber J. Tresca is a freelance writer and speaker who covers digestive conditions, including IBD. She was diagnosed with ulcerative colitis at age 16.