Diamox can give you side effects like tingling and vision trouble. Better test before the race!
In response to:
FYI: Acetazolamide is on the USADA banned substances list for both in and out of competition use. (It is used as a masking agent, so it is not like you'll get a direct benefit unless you are trying to hide the fact that you are also going to the local "Low-T" center that recently opened up.)
It is also a diuretic, so it may not be the best thing to use when running above tree line where bathrooms are few and far between. :-)