How much caffeine does it take to kill someone? Here comes the science.


A wrongful-death lawsuit filed last week against the makers of Monster energy drinks claims that 14-year-old Anais Fournier drank two 24-ounce cans of Monster in the day before she unexpectedly died late in 2011. The coroner’s report described “caffeine toxicity” as contributing to her death. Just what does it take to ingest a lethal dose of caffeine?

The answer is hard to pin down, in part because it happens so rarely, but it’s clearly a hell of a lot. In an email, Jack James, the editor-in-chief of the Journal of Caffeine Research, says that overdose for adults requires roughly 10 grams of caffeine. (People typically ingest just 1 to 2 mg/kg of caffeine per beverage.) A 2005 Forensic Science International article on two fatal caffeine overdoses in New Mexico pegs the figure closer to about 5 grams–an amount that would still require drinking more than 6 gallons of McDonald’s coffee. Whereas a normal cup of coffee might bring the concentration of caffeine in your plasma to 2.5 to 7 mg/L, the two people who died in New Mexico–a woman who might’ve used caffeine to cut intravenous drugs, and a man whose family said he ingested a bottle of sleeping pills–both had concentrations 100 times higher. (A web application called “Death By Caffeine” uses a benchmark around 6 grams per hundred pounds of body weight to estimate death, but it’s “for entertainment purposes only.”)

So if a true caffeine overdose is so rare, why has caffeine–perhaps the most widely used drug in North America–been blamed for contributing to a handful of deaths over the years? Perhaps because it almost always works in concert with other far more nefarious factors such as alcohol or heart conditions. Indeed, the suit filed in California points out that Fournier suffered from Ehlers-Danlos syndrome. According to the autopsy report, the cause of death was a cardiac arrhythmia that the caffeine brought on. But the arrhythmia was also complicated by “mitral valve regurgitation in the setting of Ehrlers-Danlos syndrome,” which affects collagen synthesis and thus multiple body systems, including the cardiovascular system.
“Caffeine toxicity of the kind experienced by Ms. Fournier (if, indeed, that is what she experienced) is not well understood,” James says. “There is speculation in the literature regarding the possibility of some individuals having a peculiar sensitivity to caffeine, but there is no clear definition or understanding of what such sensitivity might be.”

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