Acute mountain sickness (AMS) commonly occurs when unacclimatised individuals ascend to altitudes above 2000 m. Acetazolamide and Ginkgo biloba have both been recommended for AMS prophylaxis; however, there is conflicting evidence regarding the efficacy of G. biloba use. US researchers performed a placebo-controlled RCT of acetazolamide vs. G. biloba for AMS prophylaxis. They randomised unacclimatised adults to receive acetazolamide, G. biloba or placebo in double-blind fashion and took them to an elevation of 3800 m for 24 h. They graded AMS symptoms using the Lake Louise Acute Mountain Sickness Scoring System (LLS) and compared the incidence of AMS (defined as LLS score ≥ 3 and headache). Fifty-seven subjects completed the trial (20 received acetazolamide, 17 received G. biloba and 20 received placebo). The LLS scores were significantly different between groups; the median score of the acetazolamide group was significantly lower than that of the placebo group, unlike that of the G. biloba group. AMS occurred less frequently in the acetazolamide group than in the placebo group (effect size 30%; 95% CI 61 to −15%) and the frequency of occurrence was similar between the G. biloba group and the placebo group.