In healthy individuals, the only common side effect of probiotics is mild digestive discomfort, such as in the form of gas, according to the National Center for Complementary and Integrative Health. However, as of 2015, scientists still have some uncertainties about the long-term safety of taking probiotics, and more research is necessary. Taking probiotics can cause severe infections in people who have had surgery recently, are critically ill or have weakened immune systems.
Not all probiotic products contain the same bacteria strands, meaning it is possible that some products are safer than others, notes the National Center for Complementary and Integrative Health. For example, the results of one study indicated that a specific strand of Lactobacillus appears to be safe for healthy individuals above the age of 65, but the study is not sufficient evidence that probiotic use in general is safe in elderly people.
Despite claims that probiotics are helpful in managing a wide range of health conditions, there is little or no scientific evidence available, warns the National Center for Complementary and Integrative Health. There is some evidence that probiotic supplements prevent diarrhea in people who are taking antibiotics or have certain infections. There is also some evidence that probiotics may lessen the symptoms of irritable bowel syndrome. More research is necessary to establish which specific probiotics are most effective at providing these benefits and how much patients must take to achieve such benefits.