What are probiotics?

Probiotics are live microorganisms (bacteria and yeasts) found in your intestines. Similar probiotics are available in some foods and dietary supplements. Probiotics are sometimes called “good” or “healthy” microorganisms. It is thought that they help maintain a healthy digestive system and limit the growth of “bad” or “unhealthy” bacteria.

Why do people take probiotics?

The use of probiotics relate to digestive health. Although some probiotics have shown promise in research studies, strong scientific evidence to support specific uses of probiotics for health conditions is lacking. There is evidence that probiotics may be helpful in preventing diarrhea caused by infections and antibiotics, and in improving symptoms of irritable bowel syndrome. However, the U.S. Food and Drug Administration (FDA) has not approved any probiotics for preventing or treating any health problem.

Are probiotics safe?

Probiotics are similar to the “good” or “healthy” microorganisms already living in your digestive system. Medical studies have not shown probiotics to be harmful to healthy people. However, people who are very ill and people who have a compromised immune system should be cautious about eating or drinking probiotic products, or taking supplements.

Common side effects might include gas and bloating. While these are typically mild and temporary, more serious side effects include allergic reactions to the probiotics or ingredients in the food or supplement.

You should talk to your family doctor before you start taking probiotics or any type of dietary supplement. He or she can tell you if a probiotic supplement or other form

will affect any medical conditions you have. He or she also needs to know about any prescription or over-the-counter (OTC) medicines, or other dietary supplements you are taking.

How are probiotics available?

Foods and drinks that contain probiotics include the following:

  • Soy drinks
  • Yogurt
  • Acidophilus milk (regular milk enriched with a healthy strain of bacteria)
  • Buttermilk
  • Some soft cheeses (for example, Gouda)
  • Miso (fermented soybean paste)
  • Tempeh (fermented soybean cake)
  • Kefir (drink made from fermented cow’s milk)
  • Kimchi (spicy fermented vegetables)
  • Unpasteurized sauerkraut

Look for labels that identify “live active cultures” or that include the full name of the bacteria on the nutritional label. There are many different types, or strains, of probiotics available. Most of these are of the Lactobacillus and Bifdobacterium variety. For example, Lactobacillus acidophilus is a type of probiotic that can be found in yogurt and soy products.  

Probiotics are also available as dietary supplements in capsules, tablets, powders, and liquids. One commonly used supplement is acidophilus.

What are prebiotics?

Prebiotics are nondigestable ingredients that help healthy bacteria grow in the digestive system. They act as fuel for the probiotics. Prebiotics are found in foods like soybeans, asparagus, and bananas. The term “synbiotics” refers to products that combine probiotics and prebiotics. They are typically found in supplements.


This content was updated with general underwriting support from NatureMade®. Funding and support for this material have been provided by the Consumer Healthcare Products Association.


See a list of resources used in the development of this information.

Written by editorial staff

Reviewed/Updated: 10/15
Created: 01/11