A report claiming one cannabis joint is as harmful as up to 20 legal cigarettes has divided opinion in the medical world. So just how dangerous is the drug? Health and Education Editor Barry Nelson reports

WHILE cannabis is the most commonly used illicit drug in the UK, with more than two million people admitting to having used it in the past year, a leading charity claims there is still a dangerous lack of public awareness of how harmful it can be.

The British Lung Foundation (BLF) has just published a report which asserts that the risk of developing lung cancer is up to 20 times greater from a cannabis joint than a legal tobacco cigarette.

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But the report has been condemned by both the respected expert on drugs Professor David Nutt, the Government’s former chief drugs advisor, who points out that it is “unfounded inference”, and cannabis law reform campaigning group Clear, which insists it is “scaremongering and exaggeration”.

The BLF report says there are “strong associations between smoking cannabis and many lung and respiratory illnesses, including tuberculosis, acute bronchitis and lung cancer”.

It says it is also strongly associated with suppression of the immune system and heart disease.

Yet, according to the charity, there is an “alarming disconnect” between the public perception of cannabis as a relatively safe drug and the impact it can have on the lungs.

The charity states that the risk of developing lung cancer is up to 20 times greater in a cannabis cigarette than in a tobacco cigarette – yet 88 per cent of the 1,045 British people it questioned believed tobacco cigarettes pose the greater risk.

Dame Helena Shovelton, the BLF’s chief executive, said: “It is alarming that, while new research continues to reveal the multiple health consequences of smoking cannabis, there is still a dangerous lack of public awareness of quite how harmful this drug can be.

“Young people in particular are smoking cannabis unaware that, for instance, each cannabis cigarette they smoke could increase their chances of developing lung cancer by as much as an entire packet of 20 tobacco cigarettes.”

The BLF says the average puff on a cannabis cigarette is two-thirds larger and is held for four times longer than the average puff on a tobacco cigarette.

As a result, it says, someone smoking a cannabis cigarette inhales much more tar and carbon monoxide.

Cannabis is one of the most widely-used recreational drugs in the UK, with nearly a third of the population having tried it.

Dame Helena says: “We need a serious public health campaign to finally dispel the myth that smoking cannabis is a safe pastime.”

However, Prof Nutt, chairman of the Independent Scientific Committee on Drugs (ISCD), says its claims about the harm cannabis may do to the lungs are unfounded and based on only one study.

He adds that the report’s interpretation that a cannabis joint may be as carcinogenic as up to 20 cigarettes is “dubious”.

PROF Nutt also warns: “If the BLF’s misguided information is believed, people could actually be put at greater risk of lung cancer, for example by cutting down on the cannabis in their joints and padding them out with more tobacco.”

Psychiatrist and ISCD member Dr Tim Williams says that cannabis research is complicated by the fact that most cannabis is usually smoked with tobacco.

“We need to be honest and say we don’t actually know the risks associated with cannabis,” he says.

Teenage cannabis smokers have a higher risk of developing psychotic symptoms later in life, perhaps because their developing brains are more vulnerable.

However, while cannabis use has soared in the UK, he points out that levels of schizophrenia have not and there is no global effect of cannabis causing schizophrenia or psychotic illness in older brains that don’t already have mental problems.

Dr Williams says that the drug does have a higher concentration of certain cancer-causing compounds than nicotine.

However, the potential cancer risks are reduced as cannabis users generally smoke fewer cigarettes than tobacco smokers and most give up the drug in their 30s.

Evidence is emerging that cannabis is beneficial to people with multiple sclerosis (MS), says Dr Williams, and in 2010 the symptom relief drug Sativex, which includes cannabis extract, was licensed for the treatment of spasticity in people with MS.

One of the first UK patients to use Sativex, a former North-East nurse, told The Northern Echo in 2008: “This is the first MS drug I have taken which helps me and has no side-effects.

It works within about 15 minutes…it has taken me two years of misery to get this drug and I feel that is should be much easier for people with MS to get Sativex.”

SOME argue cannabis use leads to stronger drugs, such as heroin, but Dr Williams points out that early alcohol use and cigarette smoking also predicts future cannabis use.

He adds: “We can be certain that there are some elements of harm to cannabis, but when put against the harm associated with alcohol, tobacco and heroin, for example, it’s much lower.

“We have to accept there is a large amount of cannabis smoking out there, so what can we do to reduce the risk to these people?”

Apart from the health risks of cannabis, The Northern Echo reports on an almost daily basis how people are criminalised because of growing and dealing in the drug, while others are subjected to violence and intimidation because this brings them into contact with criminal gangs.

Only this week it was reported how a 34 year old man from Billingham was spared jail after a gang broke his nose with a hammer and threatened to shoot him unless he managed a cannabis farm.

Cannabis Facts

• Two million people in the UK smoke cannabis, and half of all 16 to 29-year-olds have tried it at least once.

• Cannabis was re-classified in January 2009 and is now a Class B drug. The maximum penalty for possession is five years in prison and/or an unlimited fine, or both, and 14 years in prison and/or an unlimited fine for dealing or supplying.

• About one-in-ten cannabis users have unpleasant experiences, including confusion, hallucinations, anxiety and paranoia.

• The amount of the main psychoactive ingredient, THC, in herbal cannabis varies from one per cent to 15 per cent, and newer strains, including skunk, can contain up to 20 per cent.

• Cannabis Law Reform (Clear) is encouraging those who use cannabis not to smoke it with tobacco.

• The Royal College of Psychiatrists has produced a leaflet on cannabis and mental health, available from rcpsych.ac.uk