Probiotics are live microorganisms intended to provide a health benefit when consumed in adequate amounts. They occur in some fermented foods and are sold in supplements, but products and strains are not interchangeable.

What the evidence can and cannot show

The U.S. National Center for Complementary and Integrative Health notes that probiotics have been studied for several digestive and other conditions. Results depend on the particular microorganism, dose, population and health problem. Evidence for one strain or combination does not prove that every product labelled “probiotic” will have the same effect.

Researchers are still working to identify which probiotics may help, the amount needed and who is most likely to benefit. A supplement should not be treated as a substitute for established medical care.

Reading a probiotic label

Useful product information can include the genus, species and strain, storage instructions, expiry information and the number of live organisms expected through the end of shelf life. A larger microorganism count does not automatically mean a product is more effective.

Safety considerations

For many healthy people, commonly used probiotics appear to have a history of generally safe use, although gas or digestive discomfort can occur. The risk of serious harm may be greater for people who are severely ill, have weakened immune systems, are premature infants or have significant underlying conditions.

The centre’s probiotic safety summary advises discussing use with a healthcare provider and not using probiotics to postpone medical assessment. Product quality and regulatory requirements also vary.