Last week, newspapers in the United Kingdom detailed the tragic death of 31-year-old mother of three Gemma Moss, who reportedly "died as a result of cannabis poisoning," according to The BBC.
The answer, according to medical science, is that it's extremely unlikely.
In the long history of humanity's marijuana use, not a single person has ever died from a weed overdose. According to a 1988 ruling from the U.S. Drug Enforcement Administration, a marijuana smoker would have to consume 20,000 to 40,000 times the amount of THC in a joint in order to be at risk of dying.
A 2009 study from American Scientist on the relative toxicity of recreational drugs showed that using only 10 times the "effective" dose of alcohol could be fatal, whereas more than 1,000 times the effective dose of marijuana would have to be used to be possibly fatal.
How much did Gemma Moss smoke? A half a joint. Moss was reportedly a pot smoker for years, had stopped using two years before her death, and then recently began smoking a half a joint at night for some time to help her get to sleep.
The postmortem examination showed nothing wrong with Moss' vital organs, however, medical examiners suggested that she may have had a cardiac arrest triggered by what was said to be "moderate to high" levels of the drug in her system.
Pathologist Dr. Kudair Hussein told an inquest into Moss' death that the level of cannabinoids in her blood were "0.1 to 0.15 milligrams per liter," noting that he "looked through literature and it's well known that cannabis is of very low toxicity. But there are reports which say cannabis can be considered as a cause of death because it can induce a cardiac arrest."
“The postmortem could find no natural cause for her death," said coroner Sheriff Payne, according to the UK Mirror, "with the balance of probability that it is more likely than not that she died from the effects of cannabis.”
Dr. Allen Shackelford, a high-profile, Harvard-trained Colorado physician who evaluates patients for medical marijuana from his Amarimed offices, told The Denver Post's Cannabist that he questions the medical examiners' diagnosis.
“There’s been no history of any verified reports of a death from cannabis ever,” Shackelford said. “Cannabis can cause an increased heart rate, and there’s a possibility that it could cause a problem with someone with a pre-existing heart disease — for example, somebody with an elevated heart rate. But there’s no known dose of cannabis that could kill a human.”
David Nutt, a British psychiatrist and neuropsychopharmacologist and former chair of England's Advisory Council on the Misuse of Drugs, wrote about Moss' death on his blog Drug Science and noted his skepticism about marijuana being the actual cause. Via Drug Science:
I cannot begin to understand the pathologist’s certainty that cannabis killed Gemma Moss, but neither do I wish to contradict him outright. Taking any amount of cannabis, like all drugs, like so many activities, puts some stresses on the body. Cannabis usually makes the heart work a little harder and subtly affects its rate and rhythm. Any minor stress on the body can be the straw that breaks the camel’s back, the butterfly’s wingbeat that triggers the storm. Ms. Moss had suffered with depression, which itself increases the risk of sudden cardiac death. It is quite plausible that the additional small stress caused by that cannabis joint triggered a one-in-a-million cardiac event, just as has been more frequently recorded from sport, sex, saunas and even straining on the toilet.
Peter Reynolds, leader of UK's Cannabis Law Reform (CLEAR), told HuffPost UK that science just doesn't support the Moss verdict. "There must have been another factor involved and there isn't any evidence that cannabis was the causative factor. Tragically, spontaneous cardiac arrest does occur in apparently healthy people. Cannabis is the least toxic therapeutically active substance known to man."
The New York Daily News also reached out to a number of New York doctors about the possibility of a person dying from pot overdose.
"From half a joint? That's ridiculous," Dr. Yasmin Hurd, professor of psychiatry at the Icahn School of Medicine at Mount Sinai, told the paper.
"It would be very, very, very unlikely to get a lethal dose of the marijuana if wasn't adulterated with something," said Dr. Bradley Flansbaum of Lenox Hill Hospital.
Both doctors agreed that were the pot laced with another drug, a fatality could occur, but that it would be due to the harder laced drug -- not marijuana.
"For an adult to die solely from marijuana itself, it would take a couple hundred pounds of it being dropped on their head from a tall building," said Mason Tvert, communications director for Marijuana Policy Project, to HuffPost. "Not only have researchers and doctors confirmed this, but one of the DEA's judges also arrived at the same conclusion. It's unfortunate that one doctor's mistake is raising questions about decades of conclusive scientific research."