Probiotics are live microorganisms that may provide a health benefit when taken in adequate amounts. The effect depends on the specific strain, dose, person and outcome being studied; “probiotic” is not one single treatment.
Research on strains such as Bifidobacterium animalis subsp. lactis BB-12 and Lactobacillus rhamnosus GG applies to particular preparations and uses. Results for one strain should not be assumed to apply to another product or condition.
If you are considering a supplement, check the strain identification, amount, storage directions and evidence for your reason for using it. People who are seriously ill or immunocompromised should discuss probiotics with a clinician.