Activia yogurt has active yeasty things that your body needs. Whether your body has run out of those things, you probably can't tell. But if a doctor tells you it's good in order to replace what antibiotics kill, it's probably good to try. There are other brands of yogurt with active cultures.

I've had Activia. The "bottom" line is, if you DON'T need it, it's just yogurt. It doesn't do any harm to give you something you already have. It makes a difference if your body doesn't have it. If you take it before your digestive symptoms from antibiotics start, you'll never be aware the yogurt helped anything.