Mechanisms of antimotion sickness drugs.

Unlabelled: Eight subjects, male and female, were rotated using the step method to progressively increase the speed of rotation (+2 rpm) after every 40 head movements to a maximum of 35 rpm. The end-point for motion sickness was the Graybiel Malaise III total of symptoms short of frank nausea. The drug treatments were placebo, scopolamine 0.6 mg and 1 mg, scopolamine 0.6 mg/d-amphetamine 10 mg, scopolamine 1 mg/d-amphetamine 10 mg and amphetamine 10 mg.

Results: Scopolamine increased tolerated head movements over placebo level by +81, scopolamine 1 mg + 183, d-amphetamine + 118, scopolamine 0.6/d-amphetamine + 165, and scopolamine 1 mg/d-amphetamine 10 mg + 201.

Discussion: The drugs effective in preventing motion sickness are divided into those with central acetylcholine blocking activity and those which enhance norepinephrine activity. A combination of both of these actions produces the most effective antimotion sickness medications.

Conclusions: The balance between the acetylcholine and norepinephrine activity in the CNS appears to be responsible for motion sickness.