Final answer:
Scopolamine is the most effective motion sickness medication listed as it blocks signals to the brain that cause nausea and vomiting and has fewer side effects compared to other medications.
Step-by-step explanation:
The most effective medication for preventing motion sickness among the ones listed is Scopolamine. Scopolamine works by blocking the signals to the brain that cause nausea and vomiting associated with motion sickness. While Dramamine, Benadryl, and Antivert can also be used to treat symptoms of motion sickness, they are generally less effective than Scopolamine, and may also cause drowsiness. On the other hand, Promethazine is not usually recommended for motion sickness as it has a higher risk of side effects compared to other medications.
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