Medical Moment: Dealing with Motion Sickness

Motion sickness is a syndrome that occurs in response to real or perceived motion.  Common side effects  of motion sickness include nausea, increased salivation, warmth, sweating, and a general feeling of malaise.

The symptoms of motion sickness were first described by Hippocrates.  Motion sickness symptoms frequently occur during boat travel, and the principal symptom (nausea) is derived from the Greek word for ship (naus).

The brain receives numerous inputs that are used to estimate the motion and orientation of the head.  This includes vestibular clues from the labyrinth (inner ear), visual information (from the eyes), and somatosensory cues (from the trunk and limbs).  When these three sensory cues are not congruent, a sensory conflict is generated in the brain, and it is hypothesized that this conflict underlies the symptoms of motion sickness.

For example, if the visual system indicates that a person is stationary (viewing the interior of a cabin of a ship), but the vestibular system (inner ear) senses ongoing head movements (due to motion of the ship), the vestibular and visual cues conflict and engender symptoms of motion sickness.

Motion sickness can be induced in almost all people with sufficient provocation.  Women are generally more susceptible to motion sickness than men.  Children younger than two are typically resistant to motion sickness; the incidence peaks at approximately 12 years of age, and then decreases throughout adulthood.  Expectations and other psychological factors affect the risk of motion sickness.  A controlled trial found that cadets who were told they were unlikely to experience seasickness were at decreased risk of developing motion sickness.

A number of interventions can be used to prevent or alleviate motion sickness.  Treatments are in general more effective when used for prevention rather than after symptoms have developed.

Environmental modification

Since conflicting sensory cues are believed to induce the symptoms of motion sickness, a straightforward treatment approach is to minimize the discrepancy between these cues.  This can be accomplished by viewing an earth-fixed environment during motion rather than a head-fixed environment.  For example, motion sickness on a ship is reduced if passengers view the horizon or land masses from the deck rather than their cabin.  Similarly, passengers in a car should sit in the front seat and look through the window rather than sitting in the rear and focusing on an object moving with the interior of the car (such as a book).

Medications

In general, motion sickness medications work by inhibiting the activity in the vestibular nuclei, where labrinthine (inner ear) and visual sensory cues are combined and synthesized.

Medications should be taken before motion begins, since they are less effective in relieving symptoms that have already developed.  A number of antihistamines can be used to treat motion sickness.  Dramamine (dimenhydrinate) and Bonine (meclizine) are two common over the counter medications used.  Side effects of these medications include sedation, blurred vision and mouth dryness.

Non sedating antihistamines such as Claritin or Zyrtec do not appear to be effective for the treatment of motion sickness.

Scopolamine, available as a prescription, is another commonly used medication used for the management of motion sickness.  It is most commonly administered as a transdermal patch applied every 72 hours.  Side effects include sedation, blurred vision and mouth dryness and should not be used in people at risk for angle closure glaucoma.

Ginger can also be used as an alternative to prevent motion sickness.  Trials with naval cadets found benefit with pretreatment with one to two grams of ginger.  Its mechanism of benefit may have to do with its effect on gastric motility or its effect on serotonin receptor subtypes.

Acupressure on the anterior wrist by either manual pressure or with a wrist band has been reported to be effective for motion sickness  in some, but not all controlled trials.