According to a new study published in the Journal of the Association for Research in Otolaryngology, taking oral promethazine temporarily worsened vestibular perception thresholds which could have functional implications for patients.

Findings from the study suggest that those who take this motion sickness drug should take extra precautions to avoid falls, since a patient’s ability to perceive motion, balance, and spatial orientation may be impacted. Shifts in vestibular perception thresholds have been associated with worse performance on standardized balance tests. 

Faisal Karmali, PhD, from the Jenks Vestibular Physiology Lab at Mass. Eye and Ear, and colleagues assessed motion thresholds in 10 normal, healthy individuals during two visits to the study lab separated by four days. Study subjects were randomized to either oral promethazine 25mg or a placebo at each visit. For testing, subjects underwent a direction recognition task (left vs. right) for whole-body yaw rotation, y-translation, and roll tilt passive, self-motions. 

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The results showed tilt thresholds were higher by 31% after taking promethazine, indicating a worsening of vestibular perception (P=0.005). No statistically significant changes were seen, however, in yaw rotation and y-translation thresholds. They concluded that a person’s ability to perceive motion was significantly lowered while taking oral promethazine. “People aren’t able to reliably recognize the same size motions that they could when they are not taking the drug.”

As higher tilt thresholds are associated with a higher risk of failing a balance test, study authors added that the results can hold major functional implications with respect to driving, bicycling or piloting tasks. More research is needed to study motion perception in addition to motor responses, the authors noted.

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