vasoconstrictor

Our blood vessels are constantly narrowing and widening in response to our activity or our environment, constricting in order to retain body heat and widening to get rid of excess heat. So when we're hot our skin flushes, and when we're very cold we become pale. Since the width of the blood vessels affects blood pressure, vasoconstrictors are prescribed to treat low blood pressure. Vasoconstrictors include antihistamines and amphetamines, as well as nicotine and caffeine; we commonly buy them for our runny noses and bloodshot eyes as well. The opposite of vasoconstrictors are vasodilators, which are commonly used to treat high blood pressure.