AS NURSE, chef and purser aboard a 160-foot motor yacht called the Michaela Rose, Sheila Moore knows about motion sickness. In one particularly brutal North Atlantic storm, she recalls, a crewman from the Philippines threatened to jump overboard and swim home to escape the cold sweats, nausea and retching that gripped him. During another rough stretch along the coast of Morocco, Moore prepared a sumptuous shipboard Thanksgiving dinner for 10, only to have all but one of the guests flee the table. By midnight, Moore was ministering to that last brave diner, who after several hours of being violently ill was demanding that the yacht be put into port.
Not everybody gets sick at sea. In fact, vulnerability to motion sickness varies widely. Researchers say that for about one-third of us, a simple car trip on a bumpy road is enough to trigger the queasies. Another third require more unstable conditions -- say, a ride aboard a pitching boat -- to become upset. And the rest of us can handle just about anything short of a hurricane at sea.
The currently favored theory of motion sickness is that the central nervous system can't reconcile the conflicting signals coming from the eyes, the inner ear and the rest of the body.
"You're in a ship's cabin. Your vision says you're not moving, yet your body is constantly pitching and you're having to catch yourself," explains Randall Kohl, senior research associate with the Johnson Space Center in Houston. "The brain is trying to cope with all this until a reaction comes that says, 'I can't deal with coordinating my balance in this environment!' "
At this point, the central nervous system sends chemical messages, which in turn trigger physical symptoms. These often begin with excessive salivation, yawning, heat rushes and cold sweats, and may lead to pallor, vomiting and drowsiness. You could find yourself with a severe headache, and in the worst case, dehydration, lethargy and collapse.
Advice abounds for people who suffer such symptoms: Look to the horizon. Breathe fresh air. Eat lightly and avoid too much alcohol. If you're in a car, stop, get out and let your body recover.
For those who still suffer, or who don't want to take a chance when heading out to sea, there are a number of remedies -- various over-the-counter antihistamines, introduced in the 1950s and still the most common agents of choice, and the newer patch medication, which is available only by prescription.
For most people, says Robert McCarthy, assistant professor at the Massachusetts School of Pharmacy and Allied Health Sciences, the non-prescription medications are a good place to start. More useful in mild than extreme conditions, the antihistamines include the old standby dimenhydri nate (known popularly as Dramamine), meclizine (sold under the brand names Bonine and Antivert), and cyclizine (Marezine). They work by depressing the signals from the inner ear and by quieting the gastrointestinal tract, decreasing nausea.
"All the antihistamines increase resistance -- not 100 percent, but enough to get most people through most journeys of moderate aircraft turbulence and large vessel voyages," says Charles Wood, a motion sickness researcher working with the National Aeronautics and Space Administration.
Antihistamines must be taken an hour or so before departure, since a stomach already upset will not process the medicine effectively, and another dose taken every four to six hours. There's a choice of strengths and forms -- pills, chewable tablets and liquid. But other than that, says McCarthy, "there's not a whole lot of difference between them."
For children, Wood favors cyclizine, one of the milder antihistamines. For kids 6 to 12, check the dosage on the box. If a drug doesn't list a dosage for children, don't give it to them. And for children younger than 6, motion sickness drugs are not recommended at all.
"If you have a 2- or 3-year-old who is getting carsick," says McCarthy, "try something else first -- putting them in the front seat where they can see, for instance." If that doesn't work, consult your pediatrician.
The side effects of the antihistamines vary, but may include drowsiness or dizziness. You should not take these drugs if you suffer from glaucoma, emphysema, chronic lung disease or an enlarged prostate. The drugs can aggravate these conditions, says McCarthy. And since the medication has its own sedating effects, it should never be mixed with alcohol or tranquilizers. If you are pregnant, some of the motion sickness drugs, like meclizine and cyclizine, are to be avoided in the early stages, so be sure to check with a doctor. Elderly people, like children, are also more sensitive to medications than the average adult. "Start with the lowest possible dose," says McCarthy.