Experts wait to see the smoking gun over dangers of cannabis

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With the publication of yet another report, the risk of smoking cannabis is once again in the spotlight. Sarah Freeman reports.

When the British Lung Foundation published a report which asserted the risk of developing lung cancer is up to 20 times greater from smoking cannabis than tobacco cigarettes, the organisation was braced for the backlash.

It came, unsurprisingly from cannabis law reform campaigning group CLEAR and Professor David Nutt, the man who was sacked as chief drugs adviser to the Government in 2009 after he said ecstasy and LSD were less harmful than horse riding.

The BLF commissioned the report in the wake of figures which show two million admit to having smoked the drug in the past year, in the hope of highlighting what it described as the “alarming disconnect” between the public perception of cannabis as a relatively safe and the impact it can have on the lungs. The problem it said arises from the fact cannabis smokers inhale four times longer than those who smoke only tobacco.

However Prof Nutt, now chairman of the Independent Scientific Committee on Drugs (ISCD), which aims to give ordinary people reliable information about the effects and risks of drugs, has suggested the BLF’s claims, which focused on just one study, were “unfounded inference.”

“The BLF’s worthy intentions to help us all look after our lungs can’t be doubted,” says Prof Nutt. “The report features important harm-reduction messages about cannabis smoke, specifically that if people insist on using the drug, rolling with tobacco may increase risk of harm and using a cannabis vaporiser instead may decrease harm. However, the BLF’s interpretation that a cannabis joint may be as carcinogenic as up to 20 cigarettes is dubious.

“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.”

Prof Nutt isn’t a lone voice. Dr Tim Williams, a consultant addiction psychiatrist and member of the ISCD, suggests the BLF “got their evidence slightly mixed up”, and points out: “We don’t really know whether cannabis is more harmful than tobacco, so to say that 88 per cent of the public don’t know about the risks is not true.”

Dr Williams says that cannabis research is complicated by the fact that most cannabis is usually smoked with tobacco but, like the BLF, he emphasises that more research is needed.

“We need to be honest and say we don’t actually know the risks associated with cannabis,” he says. “While the drug does have a higher concentration of certain carcinogens, the potential cancer risks are reduced as cannabis users genreally smoke fewer cigarettes and most give up in their 30s. What is known is that teenage cannabis smokers have a higher risk of developing psychotic symptoms later in life. However, while cannabis use has gone up enormously in the last 50 years in the UK, the levels of schizophrenia haven’t. It’s fair to say that there’s no global effect of cannabis causing schizophrenia or psychotic illness in older brains that don’t already have mental problems.

“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’s a large amount of cannabis smoking out there, so what can we do to reduce the risk to these people?”