Caffeine attenuates vasovagal reactions in female first-time blood donors.

The experience of vasovagal reactions during blood donation (e.g., faintness, dizziness, lightheadedness) can be a deterrent to repeat donation. Because these reactions are associated with decreases in blood pressure, caffeine was examined as a potential modulator of vasovagal reactions by virtue of its pressor effects. Using a randomized, double-blind design, 62 female undergraduate 1st-time blood donors received either 0, 125, or 250 mg of caffeine prior to blood donation. Participants who received 250 mg of caffeine had lower scores on the Blood Donation Reactions Inventory, required fewer interventions by phlebotomists for negative reactions, and reported a greater likelihood of repeat donation than participants who received placebo. These findings suggest that a moderate dose of caffeine attenuates negative reactions in novice female blood donors and may increase the likelihood of repeat donations.