Smoke without fire? Scaremongering by the British Lung Foundation over cannabis vs tobacco

The BLF is an admirable charity that promotes lung health and supports those affected by lung disease. Unfortunately, last week they produced a press release promoting unfounded claims about the harms of cannabis to the lungs. These claims were uncritically parroted from this press release as ‘news’ by the BBCChannel 4Skythe IndependentTelegraphMetroEvening Standardthe Huffington Post and more. The BLF, who wish to promote awareness of “the serious, even fatal impact [cannabis] can have on the lungs”, managed to hit the headlines with a survey about public attitudes to cannabis commissioned alongside their new report reviewing existing evidence. Surveys, with their (often unsupported) appearance of objectivity, are a popular way for groups, commercial or otherwise, to win press attention. It has worked for them before - the Daily Mail has a ten-year old article archived online reporting a virtually identical story of BLF “research” apparently showing that the dangers of cannabis are underestimated, and worse than tobacco. Then, as now, the BLF received news coverage as if they had made a breakthrough just through publishing a survey and a report of evidence. Confusingly, whilst this is the BLF's second special report on cannabis, they have never dedicated a special report to tobacco, which causes the vast majority of lung cancer deaths and many other lung conditions.

This time around, the BBC, whose science coverage usually deserves praise, rehashed the first lines of the BLF’s press release, writing “88% [of the public] incorrectly thought tobacco cigarettes were more harmful than cannabis ones - when the risk of lung cancer is actually 20 times higher”. In this sentence, as in almost every news article I have seen on the subject, almost 9 in 10 of the public are condescended to as being mistaken, but where is the evidence for this assertion that tobacco is so much kinder to the lungs than cannabis? Could the public perhaps be wiser about drug harms than the BLF and the media? I had a closer look at the BLF’s report to check their evidence. The BLF’s report itself references a great deal of scientific evidence, but it seems to be an attempt to collect evidence that supports their predetermined opinion that cannabis harms the lungs, rather than exploring the evidence to find out what the balance of findings really suggests. When the evidence they found was mixed, they came to firm conclusions that the most alarming interpretation of the most alarming evidence was true.

This is most striking in the case of the lung cancer claim that tops the press release: that a cannabis joint is 20 times as carcinogenic as a cigarette. This is an old chestnut, listed amongst Wikipedia’s list of popular drug myths. But that didn’t stop Kenneth Gibson of the Scottish National Party lodging a motion (look for S4M-03197) in the Scottish Parliament last week on 8th June endorsing the BLF’s claims and recommendations. This claim about the 20-fold cancer risk is prominent in the introductory ‘background’ information section of the BLF’s report. Here it assures the reader that the evidence explored in the report (section 3.2) shows this. But the report contradicts itself: Section 3.2 on cancer actually very reasonably says that “studies in human populations have yielded conflicting evidence on the subject: some suggest there is a link between smoking cannabis and lung cancer while others don’t [3 references]. It’s worth noting that these studies are of limited value as they looked at relatively small numbers of people and didn’t take into consideration the quantity of cannabis smoked or the effects of smoking a mixture of tobacco and cannabis. In addition, some previous evidence suggests that THC may have anti-carcinogenic effects”. Having explained, with directions to three references, that the evidence is mixed and inconclusive, the report’s writer(s) disappointingly then give a long and overgenerous account of one of the three papers referenced, a 2008 study by Aldington (a thorough scientific rebuttal of which can be found here). They then dubiously interpret the study as suggesting that a joint is as carcinogenic as 20 cigarettes. Christopher Snowdon has written a blog poston just why this interpretation is wrong. Do the BLF at least give other evidence an airing? After considering Aldington’s paper, a much smaller account is given of another of their references, which says cannabis increases lung cancer risk 2.4 times, and they do not write anything about their third reference, which found no link to lung cancer. This last study, by Hashibe et. al., looked at more people’s cannabis use over a longer time, and so has a claim to be the most valid.

Why did the BLF reference three studies then largely ignore the findings of two? We cannot doubt the BLF’s worthy intentions to help us all look after our lungs, and indeed there are harm-reduction messages that should be heard about cannabis smoke, specifically that if you must use the drug despite the risks, rolling with tobacco may increase risk of harms, and that using a cannabis vaporiser instead of smoking it may decrease harms. The BLF’s lack of care with the evidence, and the media’s lack of care in fact-checking, could have the opposite effect from their good intentions. Public confidence in science as a means of getting to the truth can only be harmed when the BBC reports “experts” mistakenly declaring that what 88% of us apparently think about cannabis is wrong. What’s more, 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, or by making parents relatively more relaxed about finding out that their teenagers smoking cigarettes every day than finding out that they smoke the occasional joint.

What can be done? The ISCD contacted the BBC on the 6th of June, but as yet the BBC have not replied or removed the inaccuracies although they have now included an alternative opinion on the subject from Peter Reynolds of Clear. The Metro, on the other hand, can be thoroughly commended for their prompt and prominent publication of critical responses to their article fromme and other readers. We will pursue further corrections, firstly by contacting editors directly, and if that fails, through the PCC. I will update readers of this blog on any progress. The ISCD's aim is for ordinary people, without scientific expertise, to be able to find reliable information about the effects and risks of drugs. With thousands of voices clamouring to be heard, each offering conflicting views, it’s a huge challenge. As I write, the BLF’s claim about cannabis cigarettes being more carcinogenic than tobacco ones has already found its way onto Wikipedia’s information about cannabis harms, so Wikipedia currently reports, on different pages, the same claim as an evidenced fact and as a popular myth. Though I trust it won’t be there long, this shows how easily misinformation can gain the stamp of truth. The ISCD website,, should help individuals who are looking for evidence-based information. Our drugs information page on cannabis provides scientifically evidenced information on the drug and its effects and harms. For information on the specific connection between cannabis and cancer, see Cancer Research UK’s balanced information. We gave the BLF the opportunity to address the inaccuracies and inconsistencies of their report which they declined, thus missing an important opportunity to address the very real harms of smoking. Public health organisations are to be commended for trying to help the general public make better choices.  Unfortunately in this case, the choice made was to confuse rather than inform.