A topic in Clinical Evidence summarizes the results of one systematic review (search date 1999, 9 RCTs, 295 people) and one subsequent trial. According to the systematic review, acetazolamide 500–750 mg daily increased the proportion of people who remained free of acute mountain sickness at altitudes above 4000 meters compared to placebo (AR 67% vs 42%, RR 1.58, 95% CI 1.27 to 1.96). The subsequent RCT (n=197) found that acetazolamide reduced the incidence of acute altitude sickness at altitudes between 4243 and 4937 meters (25% with placebo vs 12% with acetazolamide). Polyuria (33% vs 6%) and paraesthesia (43% vs 10%) were more common with acetazolamide than with placebo. There were no RCTs of sufficient quality comparing acetazolamide and dexamethasone.