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Like the other members of its family, caffeine, as a poison of sorts, can actually be toxiceven lethal. But a person would have to consume a really huge amount of caffeine to die from it. A deadly dose of coffeeor any of the other caffeine-bearing products, like chocolate or colais equivalent to 40 strong cups (5,000 milligrams) and your body would most certainly reject it before it could do any harm. An injection of this amount of pure caffeine, however, would more than likely do the trick.
It probably won't come as a surprise, then, to discover that the human body indeed responds to caffeine as it would a poisonvery similarly, in fact, to the manner in which it responds to alcohol. Liver enzymes are called on to assail the caffeine molecules and break them down as quickly as possible. This is achieved by reversing the chemical processes by which caffeine was constructed in the plants from which it comes. Groups of moleculesthe methyl groups of theophylline, theobromine, and paraxanthineare separated one by one.
This process has an interesting net effect on humans. It turns out that one of these molecules called paraxanthine is very similar to caffeine in structure and in its effect on the brain. Paraxanthine is even more potent than caffeine itself, and since 70 percent of a dose of caffeine is broken down into paraxanthine, a healthy percentage of the buzz that coffee gives us is not from caffeine at all, but from the dismantling of caffeine into paraxanthine.
As with most other drugs, everyone's body reacts a little differently to the intake of caffeine. For some, the smallest amount of caffeine is enough to keep them awake all night. Others profess to drinking teneven twentycups a day without a disruption of sleep. Caffeine is known to upset stomachs and exacerbate anxiety in some people (though not in others), but to also ease headaches and bodily pains. It's often tied to irritability, depression, nervousness, and headaches.
In short, caffeine is not everyone's cup of tea. It is no simple chemical, and the reasons for the wild variation in its effects are not rooted in mere myth, but are the result of the chemical's complicated and not altogether understood interaction with each individual human body and mind it comes in contact with.