Park, who works with those in training to be U.S. Navy flyers, relies on conditioning more than medication and says most of his subjects develop increased tolerance after a few wild flights. "One of the best countermeasures for motion sickness is adaptation," says Catherine Webb, a research psychologist with the U.S. Army Aeromedical Research Laboratory in Fort Rucker, Ala. She notes that about 95 percent of people will eventually adapt to a motion environment, citing single-day intervals between brief motion sessions as the optimal pacing.
Locke agrees desensitization can work—you can "get your sea legs," he says—but the time that such training requires has proved impractical given astronauts' busy premission schedules. It would also be tough, he suspects, for the typical civilian's sailing excursion or dive trip, and unpredictable conditions could work against the desired outcome. And as Webb notes, adaptation can be quickly lost if exposure or training are not continued.
Also, Locke is not convinced that being in control or using biofeedback are effective. In experiments with the motion sickness–inducing chair, he has not seen any difference in results based on a subject's well-being or mental state. "It doesn't matter how they feel before the test," he says. "An individual hits the point [of feeling sick] at the same time every test."
Studies of nondrug remedies such as consuming ginger and wearing wristbands that have pressure pads on them have not provided clear results. "The trick is that you have to test properly under controlled conditions to find out what works," Locke says. And so far, in his opinion, these alternative treatments have not been rigorously tested.
Sick or sleepy
Currently available medications to treat motion sickness suppress vestibular sensations or other brain processes, so as a rule, they make people drowsy or otherwise impaired. Scopolamine, for example, can cause drowsiness and dry mouth. It also affects vision, although a recent study reported that these effects did not seem to be clinically important. Scopolamine's side effects increase with repeated use and with age; Locke says elderly people can become delirious or even psychotic when taking it.
Side effects of rizatriptan can include fatigue, sleepiness, dizziness and nausea. Promethazine, or Phenergan, a traditional antinausea medication Locke has studied, is also sedating. In tests, people who took it were fairly impaired but did not seem to be aware that they were.
The type of medication, its dosage and the timing of its administration are key to maximizing effectiveness and minimizing side effects. But, Locke says, most physicians are not well versed in such details in the treatment of motion sickness.
"There's not a lot of information out there, and much of what does exist is wrong," Locke says. "So far, there's no magic bullet." Future studies could develop algorithms for the most effective and least side effect–inducing strategies for dosing, he says. Also, more research is needed on other fronts, including more conclusive studies to test theories on why motion sickness occurs; treatment for unpredictable situations translated from controlled ones; well-designed studies to test the efficacy of alternative treatments. In addition, studies could fine-tune methods of administrating medicines and develop guidelines for medical practitioners; evaluate the effects of age on motion sickness susceptibility; and identify new and better agents for treating motion sickness, including non-pharmacologic ones. "We could gain a lot from work to identify better agents," Locke says, "and to look specifically at more effective use of existing medications."