When methamphetamine enters the body, it increases in the levels of a neurotransmitting chemical in the central nervous system called norepinephrine, this chemical helps control normal function in the body’s arteries and veins, and when its levels rise, it produces a narrowing of these blood vessels that which commonly is refered to as vasoconstriction. In turn, the presence of vasoconstriction increases the amount of pressure exerted on the walls of arteries located throughout the body, including the arteries found in and around the brain.