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Why do people have adverse reactions when donating blood? Is it all psychological?
1 doctor weighed in

Dr. Mary Callahan
Internal Medicine - Cardiology
In brief: Blood donation
Sometimes people have adverse reactions when donating blood because of the needles which can cause issues, or due to the sudden change in volume.
Depending on your body size the change in volume after taking out a pint of blood can be significant. That is why they instruct you to eat and drink after giving blood.

In brief: Blood donation
Sometimes people have adverse reactions when donating blood because of the needles which can cause issues, or due to the sudden change in volume.
Depending on your body size the change in volume after taking out a pint of blood can be significant. That is why they instruct you to eat and drink after giving blood.
Dr. Mary Callahan
Dr. Mary Callahan
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