Graded ascent with adequate time for acclimatization is the best prevention
Acetazolamide prophylaxis
Indicated for patients with history of altitude illness or forced rapid ascent to altitude
Start 24hr before ascent and continue for the first 48hrs at peak altitude
Can be restarted if illness develops
Reduces symptoms of AMS by 75% in patients ascending rapidly to altitudes >8200ft
Dexamethasone
Start day of ascent and continue for first 2 days at altitude
4mg PO q12hr
Prevents and treats cerebral edema
Combination acetazolamide and dexamethasone
Small study showed combination of both (500mg SR daily of acetazolamide and 4 mg BID dexamethasone) was more effective at preventing AMS than acetazolamide alone for rapid ascent 
Ginkgo biloba
Controversial if effective; safe
Ibuprofen
Prevention - less effective than acetazolamide, better than placebo
Treatment of headache (however, important to consider that taking ibuprofen may mask symptoms)
Indicated for patients with history of altitude illness or forced rapid ascent to altitude
Start 24hr before ascent and continue for the first 48hrs at peak altitude
Can be restarted if illness develops
Reduces symptoms of AMS by 75% in patients ascending rapidly to altitudes >8200ft
Start day of ascent and continue for first 2 days at altitude
4mg PO q12hr
Prevents and treats cerebral edema
Small study showed combination of both (500mg SR daily of acetazolamide and 4 mg BID dexamethasone) was more effective at preventing AMS than acetazolamide alone for rapid ascent 
Controversial if effective; safe
Prevention - less effective than acetazolamide, better than placebo
Treatment of headache (however, important to consider that taking ibuprofen may mask symptoms)
Acute mountain sickness
Dehydration
Decompression sickness
AMS is not improved by fluid administration alone
Chronic mountain sickness
Body hydration does not influence susceptibility to AMS
High altitude cerebral edema
Exhaustion