Acetazolamide
"We used the generic form of this medicine for a quick 3-day visit to the Rocky Mountains, to prevent altitude sickness since we were time crunched and unable to acclimate slowly.  It helped us both sleep, avoided getting ill and suppressed our appetites.  We did feel some very slight dizziness/lightheadedness when we first started it, but were able to pretty much ignore it. I highly recommend it if you will be unable to acclimate - your trip will not be spoiled by getting sick."