The objective of the study was to compare the efficacy and tolerability of seven drugs frequently used for the prevention of seasickness: the drugs were namely cinnarizine, cinnarizine with domperidone, cyclizine, dimenhydrinate with caffeine, ginger root, meclozine with caffeine, and scopolamine. The design was a randomized, double-blind study with two arms. On ethical grounds, a placebo group was not included as in a previous study, in the same setting, 80% of the passengers not receiving prophylactic drugs were seasick. The setting was in Andenes (Norway) during a time period from July to September 1992. Subjects were 1741 tourist volunteers who were joining a whale safari. The main outcome measures were vomiting, malaise (modified Graybiel criteria), and subjective reports of adverse events. Follow up was possible in 1489 volunteers (85.5%). In each active treatment group, 4.1-10.2% experienced vomiting and 16.4-23.5% experienced malaise (not significant). Equally, there was no significant difference in the incidence and characteristics of adverse events reported in the various medication groups. Scopolamine Transdermal Therapeutic System (TTS) users exhibited slightly more visual problems and the agent tended to be less effective. Six of the seven medications may be recommended for prevention of seasickness; scopolamine TTS seems the least attractive.