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Cause of motion sickness still unclear

Eve Glazier, M.D. and Elizabeth Ko, M.D

Dear Doctor: What can you recommend for motion sickness? We’ve been taking the family driving a lot lately to get us out of the house, but unless I’m the one behind the wheel, the mountain roads where we live make me nauseated.

Dear Reader: There’s nothing like a bout of motion sickness to ruin an otherwise fun day. The symptoms can range from the queasy stomach that you describe to dizziness, a throbbing headache, cold sweats, anxiety and vomiting. It’s a common affliction, and we wouldn’t be surprised if the other passengers in your car aren’t suffering a bit as well.

Although the exact cause of motion sickness remains unclear, it appears to be linked to a miscommunication between what our eyes are telling us and what is being reported by the delicate structures of the inner ear. Known as the vestibular system, this is the mechanism that controls balance. When you turn your head, bend down or twist around, the resulting image you’re seeing is in sync with what your inner ear says is happening. Your physical body is in motion, but the ground is stationary. In a car on a twisty road, however, the signals get mixed. Your eyes say your body is sitting still, but to your inner ear, your body is in motion. It’s not clear how or why, but this sensory dissonance stimulates pathways in the brain that lead to the often gut-churning symptoms of motion sickness. For whatever reason, the brain has decided the body is best off purging itself, and either nausea or vomiting can be the outcomes.

For some people, medications that address the symptoms of motion sickness can be helpful. This includes over-the-counter products with dimenhydrinate, an antihistamine used to control nausea and vomiting, or meclizine hydrochloride, an antiemetic to prevent nausea, vomiting or dizziness associated with motion sickness. Take it an hour or two before you head out. If over-the-counter meds aren’t working, consider prescription medications such as the scopolamine patch and promethazine. These are also useful for symptoms of seasickness. Dimenhydrinate and meclizine hydrochloride can cause dry mouth and drowsiness. If you choose a prescription remedy, be sure to go over the potential side effects with your pharmacist.

Since you know you’re prone to motion sickness, you can take precautions before the drive. Avoid a heavy meal before you head out. Stay hydrated, but skip the caffeine, beer or cocktails. Crack a window to get a steady supply of fresh air. Opt for the front seat, where you can easily keep your eyes on a fixed point on the horizon in front of you. That helps your brain unscramble the mixed signals sent by your eyes and inner ear. Some travelers swear by ginger, available in powdered form, to ease nausea. Despite conflicting evidence about its efficacy in easing motion sickness, acupressure also has its proponents. In this method, constant pressure is applied to the insides of the wrists via specially designed elastic wristbands.

If all else fails, consider taking a turn behind the wheel. It’s not known why, but having control over the car sharply reduces the risk of motion sickness.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)


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