In February, reports filtered in from Germany that two men died of cardiac arrhythmia triggered by marijuana intoxication. At a headline's glance, the tragic deaths seemed to spoil cannabis' unblemished track record: Until that point, no cases of fatal overdose were known to science.
It should be noted, however, that these two men -- aged 23 and 28 -- did not overdose. The researchers who reviewed their deaths in the journal Forensic Science International reported that "the younger man had a serious undetected heart problem and the older one had a history of alcohol, amphetamine and cocaine abuse." Since all other causes of death were ruled out, the researchers assumed that marijuana spiked their heart rates and blood pressures, causing their hearts to fall out of rhythm.
In the absence of underlying health conditions, it is practically impossible to die from smoking marijuana. The LD50 -- the dose required to kill half the subjects in a test population -- of marijuana's active chemical THC is somewhere between 15 and 70 grams for the average human. As the University of Michigan's Mind the Science Gap described, that's "absurdly high":
"To put that in perspective, the casual user (once a month or so) generally only needs about 2-3 mg of THC to become intoxicated, while habitual users might need between five and ten times that amount. Since 3 mg = 0.003 g, a casual user would need to smoke about 5000 times their normal amount to approach a potentially lethal dose."
What chemicals are deadlier than THC? Quite a few actually. Cyanide, arsenic, and strychnine obviously top THC, but so does nicotine, caffeine, ethanol, and table salt! A convincing case can even be made that it's easier to overdose on the very essence of life on Earth: water.
Though water has a vastly higher LD50 compared to any other chemical -- roughly 90 grams per kilogram of body weight -- humans are surprisingly able to slurp down too much of it, especially when competition, peer pressure, exercise, or the drug ecstasy are involved.
In 2007, a California woman died from water intoxication after drinking six liters of water -- roughly 25 glasses -- in three hours. Writing in Scientific American, Coco Ballantyne recounted other noted deaths and issues associated with excessive water intake:
In 2005 a fraternity hazing at California State University, Chico, left a 21-year-old man dead after he was forced to drink excessive amounts of water between rounds of push-ups in a cold basement. Club-goers taking MDMA ("ecstasy") have died after consuming copious amounts of water trying to rehydrate following long nights of dancing and sweating. Going overboard in attempts to rehydrate is also common among endurance athletes. A 2005 study in the New England Journal of Medicine found that close to one sixth of marathon runners develop some degree of hyponatremia, or dilution of the blood caused by drinking too much water.
Water, of course, is easier to access than marijuana. If THC ubiquitously flowed from taps and showerheads, doubtless somebody would have found a way to overdose. As it is, you'd be hard pressed to find an average person with enough marijuana to kill himself. Thus, water's body count remains higher.