Adrenaline

A neurotransmitter or neurohormone synthesized from noradrenaline, primarily involved in the fight or flight and stress response (e.g. fear). Also known as epinephrine.

Reference:
Bear, M.F., Connors, B.W. & Paradiso, M.A. (2001). Neuroscience: Exploring the Brain. (2nd Edition). Baltimore, MD: Lippincott Williams & Wilkins.