Does the efficacy of probiotics decrease over time?

Yes, because . . . Probiotics are usually still alive, if refrigerated and stored properly all the time from production, through shipping, to being on the store shelf. The living microorganisms get weaker and die over time. The problem is that nobody can really tell how much live material was in the package to start, how much is alive when one buys it, how much survives at home, nor how much goes to one's intestine.