There was a time when getting your daily dose of caffeine meant a simple cup of coffee or tea.
Poured into a ceramic mug, the steaming liquid tended to be enough to give most people that extra burst of energy to get out the door. Back then, you'd have to drink a heck of a lot — 81 cups of brewed coffee or 317 cups of black tea, for the average 195-pound U.S. male — to reach a lethal dose. So while you might have gotten the occasional shakiness, nausea and fast heartbeat associated with ingesting too much caffeine, you were highly unlikely to die from it.
But somewhere along the way, caffeine became an obsession, a need for many Americans, and an entire industry sprang up to try to make caffeine-ingesting more efficient.
Today, caffeine comes in all shapes and formulations — Red Bull and Monster energy drinks, "Stay Awake" pills, Jolt gum. The most potent form, the pure powdered kind that's meant for people to mix into their food, is sold in bulk in bags or canisters that can cost as little as $10 per pound. A single teaspoon can be packed with as much caffeine as 28 cups of regular coffee.
Source : http://www.chicagotribune.com/lifestyles/health/ct-caffeine-overdoses-prompt-fda-to-issue-a-warning-20150909-story.html216