Originally Posted By: bobpickering
If you have a history of AMS, it probably pays to take Diamox before you go up. Otherwise, carry it and take 125 mg if and when you need it.

I am not a doctor but here's my dosage advice based on having taken diamox multiple times and having read a ton of literature...

125mg per 24 hours is the optimal preventative (prophylactic) dose. As mentioned, splitting tablets is fine. You MUST start 2-3 days before being at elevation for it to make a difference. At this dosage side effects shouldn't be more than increased urination and possibly some light tingling in extremities. (Assuming, of course, that your doctor has cross-checked vs any other conditions or medications you may have which might interact w/ diamox.) 250mg/day will give you much more pronounced side-effects with minimal to no additional preventative effect.

Since you already have the prescription you may as well take it preventatively rather than wait for any symptoms.

Taking 125mg after you are already experiencing symptoms won't do enough. At that point you need 250 or 500 / day and this means you are already in an emergency situation and side effects are the least of your worries. You need to get down from altitude ASAP and possibly get to a doctor.

I have found that doctors not familiar with mountaineering routinely get confused between the recommended dose for prevention vs. acute treatment. I had one doctor give me 500mg/day prescription for prevention which would have been WAY too much.