Diarrhea is the number one medical complaint of travelers in the first 2 weeks away from home. It is prevalent in countries with underdeveloped water purification and sanitation systems, and it attacks nearly everyone who visits the Khumbu for any amount of time. BUT it is preventable if you are careful and practice good hygiene.
Some people take prophylactic (preventative) medication to prevent diarrhea, but this may be a very risky practice. The potential side effects from some of these medications range from slightly annoying to deadly, not to mention the alteration of your natural bacterial flora and potential development of antibiotic resistance. You should make the decision to take prophylactic medications with your personal physician. I don’t advise it in most situations.
FFor climbers with diarrhea on Everest, higher camps provide even more hostile situations; stripping in the icefall or while roped at the Lhotse wall is inevitable at times, and memorable always. In 1997, a climber fell and was killed while doing his thing at C3. Always be carefully roped when leaving tent at C3, even for very short distances!
Diarrhea causes dehydration and disturbance of the mineral balance in your body. Drink plenty and add electrolyte supplement (ORS packets are widely available in Nepal.)
Since diarrhea is such a pain on Everest, sometimes you will have to take aids like Imodium to halt it. You should be careful with these aids though. If you have a bacterial infection, diarrhea is your body’s way of getting rid of the bad bacteria. Use Imodium or the equivalent only when you really have to.