When you need to take Pepto Bismol you can safely take Pepto Bismol for up to 2 days.
If the illness does not resolve within a few days or does not get better somewhat after 2 days of taking Pepto Bismol then you should see your doctor.
Do not take more Pepto Bismol than safe to do so because you can get sick and potentially die as well from an overdose of Pepto Bismol.
I find that within a few days of taking Pepto Bismol my symptoms improve.
Pepto Bismol does expire but even after the Pepto Bismol has expired it's still safe to take the Pepto.
If you do take the expired Pepto Bismol it will just be less effective than it would if it were fresh and not expired.
The expiration date of the Pepto Bismol or any other medicine is not the date after which the medication or Pepto Bismol goes “bad”.
It is the date after which the manufacturer of the medicine including the Pepto Bismol will not guarantee the product meets FDA standards for full potency and safety.
So also the manufacturer cannot guarantee if the Pepto Bismol will even work as well.
So you can take expired Pepto Bismol and it will be okay and I have done so myself but I find that expired Pepto Bismol takes longer to work than fresh non expired Pepto Bismol.