Epinephrine is a powerful chemical your body produces in moments of danger or stress. It's the substance that makes your heart pound, your muscles tense, and your mind sharpen when you're startled or scared. You might know it better by its other name: adrenaline.

Your body releases epinephrine from small glands near your kidneys when your brain detects a threat. Within seconds, it surges through your bloodstream, preparing you to either fight or run away. This is why people call it the fight-or-flight response. Your heart beats faster to pump more blood to your muscles. Your breathing quickens to take in more oxygen. You might feel suddenly alert and focused, even if you were tired moments before. Some people describe feeling stronger or faster than normal under its influence.

Doctors also use manufactured epinephrine as a life-saving medicine. People with severe allergies carry epinephrine injectors in case they're exposed to something dangerous, like peanuts or bee stings. The medicine works the same way the natural chemical does, opening airways and stabilizing blood pressure during a medical emergency. Epinephrine injectors can mean the difference between life and death for someone having a severe allergic reaction.