Vasoconstriction is the narrowing of a blood vessel due to the contraction of a surrounding muscle. It is a normal physiological response to bleeding, cold, or suddently sitting up. It is also either the therapeutic or a side effect of many pharmaceuticals including antihistaminesdecongestants and stimulants. In most cases, vasoconstriction will raise local blood pressure in the affected area.

Vasoconstriction at Wikipedia

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