Weeding out the truth (Image: Photofusion/Rex)

The first full post-mortems of people who died after smoking cannabis suggest that the drug can kill unaided.

Cannabis has been known to cause death when laced with other substances, by triggering a heart condition or by causing respiratory cancers. But whether it can be directly lethal has remained unclear. A 2011 report from the UK Department of Health says no cases of fatal overdose have been associated with cannabis.

But earlier this month, a UK coroner’s report found that a 31-year-old woman died from a marijuana overdose. So can it be fatal?


Benno Hartung of University Hospital Düsseldorf in Germany and his colleagues conducted post-mortems on 15 people whose deaths were linked to cannabis use. To rule out other factors that might have contributed to death, such as alcohol use or liver disease, they performed numerous tests, including an autopsy, a toxicology exam, genetic tests and histological analysis of all organs. “It’s a diagnosis of exclusion so you have to rule out all other possibilities,” says Hartung.

Two of the deaths could not be attributed to anything but cannabis intoxication. Both were men who died of cardiac arrhythmia – when the heart beats too quickly or slowly. The team surmises that this was triggered by smoking cannabis. Both men had enough THC – an active chemical in cannabis – in their blood to suggest they had taken cannabis within hours of death. Neither had a history of cardiovascular problems or channelopathies – diseases that increase the risk of heart problems by affecting ion channels. “We did every test we could,” says Hartung.

Long-term effects

It is not clear how cannabis could trigger arrhythmias. There might be unknown channelopathies that increase the risk of cardiac conditions triggered by the drug, says Hartung.

Even so, says David Raynes at the UK National Drug Prevention Alliance,”these deaths are rare and will remain rare. The real risks are from long-term effects on the young brain.”

Several studies show a link between cannabis use and an increased risk of schizophrenia, depression and a lowering of IQ. However, many of these studies remain contentious.

“Even though it may be rare, I hope others investigate death by cannabis intoxication in other cities,” says Hartung, “particularly in light of the increased use of cannabis for pain relief.”

Journal reference: Forensic Science International, DOI: 10.1016/j.forsciint.2014.02.001