While putzing around the Twitters yesterday I came upon an intriguing question: how much caffeine would it take to induce a heart attack? The question is a fun one given that caffeine, our widespread enjoyment of it notwithstanding, is in fact poison. The plants that produce caffeine naturally – coffee shrubs, tea bushes, kola trees – do so because it’s an effective pesticide.
So yes, caffeine can kill you. Not necessarily through a heart attack, though a high enough dose will screw up your cardiovascular system hugely. But exactly how much would one have to ingest before dying?
Well, since most of us get our caffeine via coffee, let’s try and figure out how much coffee is too much.
First: what is caffeine? It’s the street name of 1, 3, 7-trimethylxanthine, a slightly bitter alkaloid that dissolves in water. It’s prized for the stimulating effect it produces inside the human brain through a mechanism of action that isn’t completely understood. And it provided the basis for one of sitcom television’s most indelible dramatic performances.
The National Institutes of Health has a whole database running down the toxicity of chemicals like caffeine. They compiled together all the research and found that for caffeine, "an estimated lethal dose is 150 to 250 mg/kg, or 10 to 20 g." (A quick note on that unit of measurement: mg/kg, or milligrams per kilogram. That’s milligrams of the toxin per kilogram of body weight of the entity ingesting it. It’s the standard unit used to quantify what toxicologists call the LD50, which is the dose needed to kill 50 percent of a test population. Toxicology is a very grim field.)
In isolation, 10 to 20 grams isn’t a whole lot – 20 grams is less than an ounce. But your average 8 fl. oz. cup of coffee has just 95 to 200 milligrams of caffeine. So how much coffee would you need to drink to give yourself a fatal dose?
Well, for the sake of argument, let’s assume you’re a smaller person of frail constitution, and a lethal dose of caffeine for you is 10 grams. Let’s also assume that, despite your overall frailty (or perhaps because of it) you drink the high-octane coffee – 200 milligrams of caffeine per 8 fl. oz. cup. Your weak, spindly ass would have to drink 50 cups of coffee (three gallons plus another pint) before you kick off.
Of course, that assumes that you hung on to every molecule of caffeine you ingested. But guess what? You won’t hang on to every molecule of caffeine. Again, from the NIH profile on caffeine toxicity: "Spontaneous emesis often serves to limit the amount of caffeine available for absorption." Because you're curious, "spontaneous emesis" is labcoat-speak for "uncontrollable vomiting," which is a symptom of mild caffeine toxicity.
So, basically, it's difficult to build up a lethal store of caffeine in your system because your body will puke it out.
But let’s say regular old drip coffee just doesn’t do it for you. You need something stronger. So you roll into Dunkin Donuts for a monstrous 20 fl. oz. coffee with a Turbo Shot of espresso and 436 milligrams of caffeine. You’ll want to know how many you can drink before jittering yourself into an early grave. Well, to get to 10 grams of caffeine, you would have to put back 23 of those bad boys.
What about just straight up espresso? A 2 fl. oz. shot of Starbucks espresso imparts 150 milligrams of caffeine. In order to reach the 10 gram lethality threshold, you’d have to order 67 shots from your barista – just over a gallon’s worth of espresso.
Of course, all this math is rudimentary and makes a lot of assumptions that someone who actually performs accurate science would never make, but it at least gets across the implausibility of overdosing on caffeine via Maxwell House. No matter how you prepare it, to get to the low estimate of caffeine’s lethal dosage, you have to drink an extraordinarily large quantity of coffee over a very short period of time.