<p>Per sensory conflict theory, vestibular sensory information has been proposed to drive motion sickness given deviations from central expectations. However, the consistency of motion sickness with quantitative predictions of manipulated vestibular sensory conflict remains untested. Here, we evaluated motion sickness symptoms within 10 participants exposed to galvanic vestibular stimulation (GVS) designed to manipulate vestibular sensory conflict during passive physical translations. Using a computational methodology, equal and opposite GVS waveforms were designed to reduce (Beneficial) or increase (Detrimental) motion sickness while controlling all other sources of sensory information and central confounds. Beneficial GVS produced a 26% motion sickness reduction, and Detrimental GVS produced a 56% increase (<i>p</i> = 0.0055), demonstrating the causal role of vestibular information in human motion sickness. Validating our predictions, this finding supports the theory that vestibular sensory conflict mediates motion sickness and facilitates new methods and countermeasures for mitigating motion sickness during transportation and in virtual environments.</p>