1819

Caffeine

Pierre-Joseph Pelletier (1788–1842), Friedlieb Ferdinand Runge (1795–1867)

Caffeine is the world’s most widely used consciousness-affecting drug. It had been clear for centuries that there was some sort of stimulant in coffee, tea, and other plant extracts, but it wasn’t until 1819 that German chemist Friedlieb Ferdinand Runge isolated what he called Kaffeebase (coffee base) as a pure substance. It was independently discovered in France not long afterward (where the name caffeine was given to it) by researchers looking for quinine in coffee beans (no such luck). A few years later, a similar compound, theine, was reported to be isolated from tea. This turned out to be the exact same substance, however, and it gradually became clear that a wide variety of plants produced it.

But why would plants bother spending their metabolic energy making caffeine? Because it’s a mild pesticide, for one thing, and it also inhibits the growth of some types of seeds nearby in the soil. Research suggests that it increases successful return visits by honeybees and perhaps other pollinators, too—an effect that coffee shops have found very profitable to exploit with their human customers.

Technically speaking, coffee shop customers are imbibing an adenosine receptor antagonist. An antagonist is a compound that blocks a receptor (a cell-surface signaling protein) from setting off the downstream signal inside the cell. The opposite sort of compound—one that binds and then causes the signal—is called an agonist. Adenosine (which is also found as a part of the structure of adenine, the A letter of the A, C, G, T genetic code in DNA) generally acts to suppress nervous system activity in the brain, so blocking its receptors with caffeine keeps that from happening. Too much blockade of the adenosine receptors can bring on the well-known side effects of nervousness, irregular heartbeat, and difficulty sleeping. Its lethal dose, fortunately, is too high to conveniently drink—at least seventy-five cups of coffee, all at the same time.

The most widely used stimulant in the world is not seen as an optional substance for many of its users.