The efficacy and effectiveness of drinking interventions to reduce vasovagal reactions in blood donors: A systematic review and meta-analysis.

Pre-donation plain water ingestion or isotonic drink probably results in a large reduction in on-site and off-site VVRs. Pre-donation water ingestion with caffeine consumption or salt supplementation may result in a VVR reduction, compared to water ingestion only. Future large trials are required to increase the certainty of the effect of these and other interventions in the prevention of VVRs.