Noradrenaline molecule. Computer graphic of the neurotransmitter noradrenaline, or norepinephrine (formula C8. H11. N. O3). The atoms (tubes) are colour- coded: carbon (yellow), oxygen (red), nitrogen (blue) & hydrogen (white). Noradrenaline is a substance that transmits messages in the nervous system. It has effects on the heart, blood vessels, intestines, liver and bladder. It is also used as an emergency drug to restore dangerously low blood pressure or to treat cardiac arrest, when it is injected into a vein or directly into the heart.