The ships are very large and have stabilizers, most never get sick. Sometimes we play a game where the winner is the first person who can identify when the ship starts moving. However, if they are calling for high seas then some will get sick. I've sailed about 20 days and only 1 night was rough. If someone is planning on taking any meds, I advise trying it for a few days before sailing. You don't want to be a zombie while everyone else is having fun. Even "non" drowse medicine effects many people.