Well, yes it does, but it can also cause drowsiness and other un desirable side affects. Unless you KNOW you will get sea sick, I would try to go without medication. The bigger ships are much more stable than you might think. Another possible solution is taking Ginger pills (you can get them from health food stores and probably your local drug store). My mother gets seasick, and on our last cruise, she started taking the ginger pills a couple days before and during and had no problems until about the 3rd day of the cruise when she had "forgot" to take them. She started fealing bad and rememebered that she did not have her pills and went back to her cabin and took them. She had to take a short nap, but afterwards she felt normal again.. So, you can try them if you don't want to "risk it" and don't want to take the chance on the Dramamine causing you to be sleepy (you could do the non-drowsy formula but I always seems to find the non-drowsy versions of medicines to also be "less effective" too.
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise, Magic 1/14, Freedom x 2 6/14
NCL Dream October 2006, RCCL Mariner OTS June 2007, Celebrity Silhouette 2013