Alcohol is much more deadly than cannabis, a study has found.

Scientists compared a wide range of drugs using calculations based on known lethal doses of the substances and the amount a typical person used.

They found that for individual exposure, alcohol, nicotine, cocaine and heroin all fell into a category of lethality classified as "high risk".

Other drugs including amphetamine, methadone and MDMA (ecstasy) fell into the "risk" category, but active cannabis ingredient THC was not considered even this harmful.

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At the population level, only alcohol fell into the "high risk" bracket while cigarette smoking was placed in the "risk" group.

All other chemicals studied in the population analysis - opiates, cocaine, amphetamine-type stimulants, ecstasy and benzodiazepines - fell outside the "risk" category and cannabis was nowhere near this threshold.

The study authors, led by German Dr Dirk Lachenmeier, wrote in the journal Scientific Reports the results confirmed "that the risk of cannabis may have been overestimated in the past. In contrast, the risk of alcohol may have been commonly underestimated".

The researchers used a measurement called margin of exposure (MOE), defined as the ratio between the lethal dose of a substance derived from animal studies and estimated human intake.

Lethal doses ranged from two milligrams per kilogram of bodyweight for heroin to 531 milligrams for alcohol.

A "high risk" category was defined as an MOE of less than 10 and a "risk" category as less than 100.

On the population scale, cannabis had an MOE of more than 10,000 - well outside the limits of "risk".

- PAA