Epinephrine, also known as adrenaline, was the first hormone to be discovered. It is produced continuously in small amounts by the adrenal glands, which are endocrine glands located on the kidneys. Triggered by anxiety, danger, or other stress, the brain sends acetylcholine messages to the glands, which respond by increasing epinephrine production. This in turn increases alertness, energy level, heart rate, blood pressure, and strength. This body state is known as "fight or flight," in which a person's physical strength increases making him able to combat the problem at hand ("fight") or escape the situation quickly ("flight").

The power of adrenal extracts was first observed by the British physiologist Edward Sharpey-Schafer. In 1894, he injected an adrenal extract into an experimental animal, causing its blood vessels to narrow and forcing an increase in blood pressure. Japanese-American chemist Jokichi Takemine and Sharpey-Schäfer's colleague isolated epinephrine in...