Adrenaline

Adrenaline is a hormone made in the inner part of the adrenal glands, which sit on top of your kidneys. Evidence: solid In America it's called epinephrine; same thing. Evidence: solid When something startles or threatens you, nerves from the brain signal the glands and they release it into the blood within seconds. Evidence: solid It makes the heart beat faster, raises blood pressure, speeds your breathing, opens the small airways in the lungs, and frees sugar and fat from storage for fuel. Evidence: solid It's broken down fast: half of it is gone from the blood within a few minutes. Evidence: solid Given as a drug, it causes a racing heart, shakiness and anxiety, which is roughly the rush you know. Evidence: solid

Its close cousin noradrenaline does much of the same work, but mostly as a messenger released by nerves, straight onto the heart and blood vessels, and inside the brain. Evidence: solid Adrenaline in the blood barely gets into the brain. Evidence: solid In rats, its effect on memory for charged moments seems to travel up the vagus nerve and end as noradrenaline inside the brain. Evidence: decent Cortisol comes from the outer part of the same glands and is the slow partner. Evidence: solid In lab stress tests it peaks 21 to 40 minutes after the stress starts, long after the adrenaline surge. Evidence: solid

Where it gets oversold: the "adrenaline junkie". People who chase thrills do share a measurable trait, sensation seeking, the appetite for new and intense experience, and it's partly inherited. Evidence: decent The biology proposed for it involves brain chemicals such as dopamine and noradrenaline, not a craving for adrenaline in the blood. Evidence: worth trying Doctors don't recognise adrenaline addiction as a condition. Evidence: solid

Its main medical use: an adrenaline auto-injector, EpiPen being one brand, is the first treatment for anaphylaxis, a severe allergic reaction. Evidence: solid It opens the airways and holds up blood pressure. Evidence: solid If you or someone with you carries one and needs it: use it, call an ambulance and say it's anaphylaxis, then lie down; raise your legs, or sit up slowly if breathing is hard. No better after 5 minutes: use a second injector if there is one. Don't stand or walk, even if you feel better. Evidence: solid