Promethazine Effects on Motion Sickness During Altered Gravity Induced by Parabolic Flight

Astronauts commonly experience space motion sickness, which can impair astronaut performance and safety. Pharmaceuticals are frequently used to reduce space motion sickness symptoms but have not been extensively studied in partial gravity. In this research effort, we investigated the impact of oral promethazine on motion sickness during parabolic flight.

We collected motion sickness scores from 12 subjects (6 women) during parabolic flight. Each subject participated in two flights-one 0-G flight and one partial g flight-experiencing 10 parabolas at 0 g, 0.25 g, 0.50 g, and 0.75 g. Half of the subjects, counterbalanced by gender, were given 25 mg of oral promethazine before flight and the other half were given a placebo. Motion sickness scores were collected preflight/postflight and during flight.

Pensacola Motion Sickness Questionnaire scores for the placebo group increased from 2.0 (1.55) preflight to 9.17 (5.42) postflight for the 0-G flight, but not for the partial g flight. Subjects in the placebo group reported motion sickness for 51.8% of parabolas compared to 12.6% of parabolas for the promethazine group. All placebo subjects reported some level of motion sickness during flight, while four of the six subjects who received promethazine reported no motion sickness at all.

Promethazine was effective at mitigating motion sickness symptoms in both 0 g and partial g. Microgravity conditions (0 g) may be more provocative than partial gravity, possibly due to the greater magnitude of sensory conflict. Further research should continue to investigate motion sickness as a function of hypogravity level. Abbott R, Weinrich MM, Keller NW, Wright TJ, Dunbar BJ, Denise P, Kennedy DM, Diaz-Artiles A. Promethazine effects on motion sickness during altered gravity induced by parabolic flight. Aerosp Med Hum Perform. 2025; 96(11):976-984.