The best remedy is prevention.
Motion sickness is caused by repeated rhythmic stimulation of nerve fibers deep inside the ear.
It worsens when visual and inner ear cues conflict. For example, reading on board provides a visual reference of stability, but the body feels the movement of the boat. On the high seas, the motion of the boat can lead to unpleasant signs and symptoms that include nausea, vomiting, sweating, fatigue, and vertigo. Getting used to the motion of a boat can take from 48 to 72 hours. And, while getting your sea legs will decrease the incidence of motion sickness, two to three days can be a long time out of commission whether you're participating in America's Cup, out for a day of sailing or embarking on a 10-day cruise.