Harvard Heart Letter

Ask the doctor: Can I keep myself from fainting when I have blood drawn?

Ask the doctor

Can I keep myself from fainting when I have blood drawn?

Q. I want to donate blood, but I faint or come close to it nearly every time I have blood drawn at the doctor's office. Can I do anything to keep myself from fainting?

A. Fainting when having blood drawn is very common. Doctors call this a vasovagal episode. These are caused by the sight of blood, an injection, standing up for too long, or other triggers that stimulate the vagus nerve. It slows the heart rate and causes blood vessels to dilate. The sudden drop in blood pressure means not enough blood gets to the brain. Complete or near loss of consciousness for a few seconds often follows.

I teach my patients who have experienced these frightening or aggravating episodes some tricks that can help minimize their chances of fainting when they know they are going to be in circumstances that put them at risk, such as donating blood.

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