Human Systems Integration Division @ NASA Ames

"INTRODUCTION: The purpose of this study is to extend our understanding of the mechanisms by which pharmacological treatments improve motion sickness and space motion sickness tolerance and their impact on cognitive function.
METHODS: Twelve men, ages 30 to 40 years, participated in this study. All subjects participated in four experimental conditions separated by one week intervals: a training day (no injections), a 25 mg, a 50 mg intramuscular injection of promethazine and a placebo injection. During each daily session, subjects were given four repetitions of three cognitive task batteries. On the training day baseline data were collected and subjects were trained to a performance plateau on each task. For the remaining days of the study, the order of drug or placebo injections were counterbalanced and a double-blind procedure was used. Physiological responses of heart rate, respiration rate, skin conductance level, finger pulse volume and hand temperature were continuously recorded in ambulatory subjects throughout each day (approx. 8-hrs). Daily samples of blood and saliva were also collected.
RESULTS: Statistically significant reductions in performance were observed across most cognitive and psychomotor tasks on days when subjects were given 25 mg or 50 mg injections of promethazine as compared to their placebo day (p<0.01). Analyses revealed no significant difference in performance in performance between the two doses of promethazine. Regression equations indicated the equivalent of performance decrements associated with blood alcohol levels (BAL) of 0.06% for 25 mg injections and 0.11% for 50 mg. A significant increase in tolerance to rotating chair motion sickness tests was found for both doses. Increases in motion sickness tolerance with promethazine were associated with lower autonomic response levels (e.g., a significant decrease in skin conductance level).
CONCLUSIONS: These data show that effective doses of promethazine used to counteract motion sickness may significantly impair susceptible individuals with respect to operational performance. Physiological data may be used to identify those subjects most susceptible to effects of medication. This work may contribute to the assessment of individual differences in effectiveness of the promethazine now used by aerospace crews as a countermeasure for space motion sickness."