What are the side effects of taking probiotics?

The first few days of probiotics are often the most honest part. For most healthy people, probiotics are well tolerated. Digestive side effects such as gas, bloating, and loose stools can happen when starting probiotics, and they are usually temporary.

Some products may feel different depending on the strain, dose, and person. Because probiotic effects can vary by strain and person, some people may tolerate one product better than another.

Serious side effects are rare in healthy adults but have been documented in vulnerable patients, including those with serious illness, compromised immune systems, or central venous catheters. Anyone in those groups should talk to a doctor before taking probiotic supplements.

Probiotic supplement regulation varies by country and is often less strict than drug regulation. Independent testing has found that some probiotic products do not always match their label claims, which adds uncertainty around both effects and safety. In the US, the FDA classifies most probiotics as dietary supplements rather than drugs, meaning manufacturers generally are not required to prove efficacy before selling them, and pre-market oversight is more limited than for drugs.

Fermented foods have been consumed across cultures for thousands of years as part of traditional diets. Modern probiotic safety concerns are especially important for vulnerable patient groups.