Is cannabis more dangerous than alcohol?

The study by King’s College London found that smoking “skunk-like” cannabis triples the risk of psychosis. The drug was linked to 24 per cent of new psychosis cases, according to the research.

The researchers say there is an “urgent need” to inform young people about the risks of strong cannabis. But what about alcohol?

Sir Robin Murray, professor of psychiatric research at King’s College London, told Channel 4 News: “Most people who drink alcohol do it moderately and enjoy it. Most people who smoke cannabis do it moderately and enjoy it.

“But if you drink a bottle of vodka each day it won’t be good for your health, the same with a large amount of cannabis.”

Physical damage

Professor Murray said that in terms of physical damage, alcohol was more dangerous.

“In absolute terms, far more people die of alcohol than cannabis. It’s very difficult to kill yourself from cannabis. It may make you do some crazy things, but you’re not going to get kidney or liver disease from cannabis.

“In terms of the psychological problems it’s different. If you drink heavily you’ll get dementia eventually. But with cannabis, there’s still a dispute.”

Professor Murray said there were relatively few studies on the psychological effects of cannabis, and there was “still an argument” about whether the cognitive impairment of a cannabis user returns to normal after heavy use.

Psychological damage

“In terms of hallucinations that is much more common with cannabis. If you’re lucky you’ll recover. But if you smoke cannabis for many years you may develop schizophrenia.”

Comparing the damage to non-users and society is difficult, said Professor Murray, mainly because one drug is legal and the other is not.

“At present, alcohol does much more damage than cannabis. But of course a huge proportion of the male population is drinking every day – sometimes heavily. Nothing like the same proportion are smoking cannabis every day.”

In 2010, a study published in the Lancet on behalf of the independent scientific committee on drugs found that heroin, crack cocaine and methamphetamine (crystal meth) were the most harmful drugs to individuals.

The most harmful drugs to those in contact with users were alcohol, crack cocaine and heroin.

Above: Drugs ordered by their overall harm scores, according to research by the independent scientific committee on drugs

The most harmful drug overall was found to be alcohol, followed by heroin and crack cocaine. Cannabis came eighth on the list.

The report was co-authored by Professor David Nutt, who was sacked as the government’s chief drugs adviser in 2009.

The findings of the study contradicted the government’s drugs classification system. The report’s authors claimed that their data showed that “the present UK drug classification system is not simply based on considerations of harm”.

Professor Murray pointed out that it is hard to find people who smoke cannabis who do not drink alcohol – and that makes it hard to study the effects of both drugs.

“The problem is that people who drink a lot are more likely to smoke as well – the two tend to go hand in hand. If we were able to cope with alcohol then it would be fine to legalise cannabis – but we can’t [cope with alcohol].”