Babette gave a pretty good reply...except that she did forget to relate that Bonine (meclizine) can possibly cause drowsiness also. The incidence is not as high with Bonine (~1-5%) as with Dramamine (dimenhydrinate; ~12-18%), Both have about the same relative effectiveness in preventing sea sickness. The big benefit in taking Bonine or other meclizine products over Dramamine/dimenhydrinate products is that you only need to take Bonine once or twice a day, where Dramamine should be taken every 6 hours.
Hope this helps!
John Burns R.Ph.