Noradrenaline (norepinephrine)

Noradrenaline is the main neurotransmitter of the sympathetic nervous system. We associate this with our fight-or-flight mechanism and moderation of other physical actions such as heart rate and blood pressure. Too little noradrenaline and we become sleepy and lethargic. Too much and our thoughts run away with us, we become twitchy and nervous, our hands and feet go cold and our blood pressure climbs.