Treating and Preventing Motion Sickness

Motion sickness, a common problem in travelers by automobile, train, air, and particularly sea, usually causes mild to moderate discomfort but in severe cases can be incapacitating. It affects up to half of children traveling in automobiles or airplanes and almost 100% of boat passengers in very rough seas. Small boats and cars tend to be the most provocative stimulus for motion sickness. Motion sickness is more common in women (especially during pregnancy or menstruation), children ages 2-12 years, and persons who have migraine headaches, but little is known about individual susceptibility. Head position and movement are sensed by the vestibular organs, the semicircular canals (angular acceleration or rotation) and otolith organs (vertical acceleration), in the inner ears. The vestibular organs generate signals that are transmitted to the central nervous system via cranial nerve VIII. Proprioceptors and visual receptors also send signals to the central nervous system about the body's relative position in space, but the vestibular system plays a critical role in the development of motion sickness. The signs and symptoms of motion sickness occur when sensory information about the body's position in, or movement through, space is contradictory or contrary to prior experience.

Classic symptoms of motion sickness include abdominal discomfort, nausea, vomiting, dizziness, pallor, and cold sweats. Delayed stomach emptying and changes in normal gastric rhythm have been associated with stomach symptoms.

Travelers who are susceptible to motion sickness can reduce symptoms by minimizing situational triggers and engaging in certain behavioral countermeasures: choose seats with the smoothest ride, usually the front seat of a car, forward cars of a train, center of a boat, and the seats over the wings in an airplane; focus on distant objects or keep eyes closed instead of reading or looking at something inside the vehicle; minimize head movement; and, if necessary, lie supine. Symptoms usually improve substantially within 15 minutes of stopping motion, when stomach motility has returned to normal. Travelers with repeated exposure to similar types of motion within a short period of time may develop tolerance or adapt to that motion.

Medications that may ameliorate symptoms of motion sickness include anticholinergic agents and antihistamines. For the prevention of motion sickness symptoms, medications are available in either oral or transdermal formulations. All oral medications should be taken at least 30-60 minutes before travel to allow adequate absorption time, as absorption may be impaired by the gastric dysmotility caused by motion. Choice of medication is based on trip duration, underlying medical conditions, concerns about sedation, and personal preference.

Scopolamine, an antimuscarinic agent that blocks cholinergic input from the vestibular organs to the CNS, is available in oral and transdermal preparations. Transdermal scopolamine is appropriate for longer voyages and may lessen severity of symptoms in all common modes of travel. One patch should be applied to the bare area behind the ear at least 4 hours before departure and changed every 3 days as needed. The patch should be applied 8 hours before departure to obtain maximal effect. Oral scopolamine is effective for 6-8 hours and can be used for short journeys or for the interval between application of the patch and onset of effectiveness. Transdermal scopolamine is associated with fewer side effects than oral scopolamine. The most common side effect is dry mouth, which is experienced by up to two-thirds of travelers and is a frequently cited reason for discontinuation of use. Other side effects include blurred vision (especially for persons with hyperopia), dilated pupils, reduced visual accommodation, and bradycardia, all of which may appear or worsen 24 hours after patch application and with successive patch uses. Scopolamine is less sedating than the antihistamines and has not been shown to adversely affect psychomotor performance.Travelers may have rebound sensitivity to vestibular stimulation following patch removal and may experience withdrawal symptoms of headache, nausea, vomiting, and dizziness.

Antihistamines used for the prevention of motion sickness include oral dimenhydrinate, diphenhydramine, promethazine, meclizine, and cyclizine. Promethazine primarily decreases nausea and may be more effective than other antihistamines, but it is the most sedating medication. Meclizine is less sedating and requires only once-a-day dosing, because its duration of action is up to 24 hours. Compared with dimenhydrinate (50 mg) and meclizine (50 mg), promethazine (25 mg) has the greatest adverse impact on psychomotor performance, both in severity and duration of side effects. Dimenhydrinate (100 mg) has also been shown to impair psychomotor performance compared with placebo.

All antimotion sickness medications can impair alertness and must be used with caution by persons operating vehicles or heavy machinery or engaging in underwater activities. This effect is additive with alcohol and other central nervous system depressants. In addition, because these drugs all have anticholinergic properties, they should be avoided in travelers with narrow-angle glaucoma, gastrointestinal obstruction, or urinary retention (e.g., prostatic hypertrophy); they should be used with caution by travelers with cardiovascular, pulmonary, liver or kidney disease. Only dimenhydrinate and diphenhydramine are recommended for use in children. They may cause paradoxical excitation and should not be used in children <2 years of age.

Nonpharmacologic remedies for motion sickness may benefit some persons but have not been proven consistently effective. Ginger has been shown to relieve pregnancy-related nausea and vomiting, but there is conflicting evidence about its use in motion sickness. Differences in sources and preparations of ginger may account for some of the variability. Pressure on the P6 neiguan acupuncture point of the wrist provides relief of nausea in pregnancy and after chemotherapy, but evidence for efficacy in motion sickness is contradictory.