Norepinephrine (Norep)

Norepinephrine or noradrenaline is a chemical produced within the humanoid nervous system. It acts as a neurotransmitter that affects the part of the brain that controls the fight-or-flight response, which in turn, increases the heart rate. In pharmaceutical form, it is sometimes abbreviated norep. (TNG: "Skin of Evil", "Who Watches The Watchers")

In 2372, the Doctor found elevated levels of norepinephrine in Lon Suder, which suggested increased aggressive tendencies. However, he also noted that Suder's levels were not significantly different from any of the other former Maquis crew. (VOY: "Meld")

The Clown, a manifestation of fear in Viorsa's virtual reality stasis system, metaphorically chopped his victims' heads off by raising the amount of norepinephrine in their bodies to such extreme levels that they suffered massive heart attacks and died. (VOY: "The Thaw")