Yes, you do need to be sure that the culture is live and of high enough count...so a health food store with a refrigerated variety of choices would be best...
...or in a pinch, I think a Kefir drink or Yakult from the dairy section of your supermarket would be a good choice.
"Courage is not the abscence of fear, it is feeling afraid and doing it anyway!"
"Worrying does not empty tomorrow of its troubles...it empties today of its strength."
Corrie Ten Boom
Panic Syndrome recovery due to CBT