Probiotics

It depends on the strain and the reason you are taking it. A review of 249 trials found effects are specific to both, and many products have no trial of their own. Some uses have signals, like less diarrhea after antibiotics and certain IBS symptoms, but confidence is often low. In healthy adults, probiotics did not change stool bacteria diversity.

Short-term trials found no more side effects than control, so weeks of daily use has not been shown unsafe. That is weaker than it sounds: reviews found harms were often poorly reported, and long-term effects are largely unknown. Case reports describe rare bloodstream infections, mostly in people with compromised health. If your immune system is weakened, ask a doctor first.

No trial in people has settled this. In one lab model of the upper gut, a four-microbe capsule survived best taken with or just before a meal and worst 30 minutes after one. That is one product in a simulation, not proof of a schedule. Pick a time you will keep and follow your label.

There is no official daily amount, and a bigger CFU number is not better by itself. A review of dose-response studies found that whether more helps depends on the outcome, with no clear relationship for most. One trial of a single named strain used 10 billion CFU a day for 4 weeks. Match the strain to its own trial.

Not automatically. Experts define fermented foods by how they are made and say they are not the same thing as probiotics. A food counts as a probiotic source only if its live microbes are identified and have a documented benefit. One review found no randomized trials of kombucha, miso, kimchi or tempeh for gut effects.