In my travels I became friends with an RN (Registered Nurse) who shared some advice with me to help me stay well. I am sharing some of that advice — about what to do for diarrhea — here. However, you must know that I am not a medical professional, this advice does not replace a doctor’s advice, and if you take this advice you may not hold me responsible for the outcome.
If, as you are traveling, you develop diarrhea, but do not have blood involved:
For the first day just take Pepto Bismal. If it helps keep taking it.
On the second day if it is slowing down, just keep taking the Pepto Bismal.
On the third day if still getting better, keep taking the Pepto Bismal.
If you are not getting better by now and are not allergic to antibiotics, take Ciprofloxin 500mg 2x a day for 3 days. (In prescription form this looks like: BID x 3 days.)
If still not better you may have Giardia so take Metronidazole (trade name, Flagyl). I was not given a recommended dosage for this. You can learn more about Metronidazole, including the other names it is marketed under in the world, in this Wikipedia article.
Only take Immodium if you MUST get on a plane/bus/submarine or such and must get rid of your diarrhea for that time.