Illustration of norepinephrine (noradrenaline, blue) molecules in the blood. Norepinephrine acts as a stress hormone and neurotransmitter. As a hormone, noradrenaline is formed in the adrenal gland (adrenal medulla) and increases heart rate and blood pressure by constricting blood vessels. As a neurotransmitter, it is produced in the locus caeruleus of the brain and has a role in increasing alertness, wakefulness, and concentration, among other functions.