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Presyncope (and more serious but less common, syncope) can occur postvaccination. Drinking water before blood donation has been shown to ameliorate these negative reactions in adolescents. To determine if water consumption also reduces postvaccination symptoms, researchers randomized 1800 adolescents (ages 11–21 years) scheduled for one or more intramuscular vaccinations to receive usual care or to consume as much water as they could from a 500-mL bottle. After vaccination, patients were observed for 20 minutes and completed a symptom survey.
Almost two thirds of patients drank 500 mL and three quarters consumed more than 250 mL. No instances of syncope occurred in either group. There were no significant differences in rates of presyncope be…