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Cannabis still isn't as addictive as heroin, no matter what the papers say

Some poor science reporting in the papers this week in response to a review of the literature on the risks of marijuana consumption.

There should be a rule when it comes to reporting the findings of a scientific study: if the article doesn't link to the paper, it's probably trying to stop you from reading it for yourself.

This is extremely applicable to some of the coverage in the papers this week of a new study by drugs researcher Wayne Hall, which looks at the cumulative findings of studies of the effects of cannabis usage from 1993 to 2013. Hall is the director of the Centre for Youth Substance Abuse Research at the University of Queensland, Australia, and an advisor to the World Health Organisation on drug issues - credentials which the Daily Mail has been keen to emphasise in its melodramatic writeup that "demolishes claims that smoking pot is harmless". The Mail's deputy editor, Tony Gallagher, was pretty strident about his paper's front page this morning too:

Over at the Telegraph it's arguably even worse, with the headline claiming that cannabis is "as addictive as heroin". Hall's study, published in Addiction, does conclude that cannabis has some nasty effects on human health - but it doesn't claim it's as addictive as heroin. (Really, it doesn't - you can read it for yourself here.)

What Hall specifically did in this paper is compare what we know now with what we knew in 1993, across a number of different categories. It isn't a meta-analysis - that's when a study assigns a statistical weight to the findings of a number of other studies and effectively finds an "average" of their results. This paper is systemic review, so while Hall cites other meta-analyses, he doesn't do any himself.

Here's a quick rundown of his conclusions:

  • If you're high, you're two to three times more likely to crash your car
  • If you smoke weed when pregnant, it might reduce your baby's birth rate slightly
  • There's no clear pattern that smoking when pregnant causes birth abnormalities
  • Smoking regularly as a teenager could lead to a slight drop in IQ in later life
  • Teenagers who smoke weed do worse in school
  • Those who smoke marijuana are more likely to do other drugs, including tobacco and alcohol
  • Regular cannabis smokers run a one in ten chance of becoming addicted
  • That chance is one in six if they're adolescent
  • Smoking cannabis could double the risk of developing schizophrenia or psychosis
  • There is a correlation between cannabis use and increased suicide risk
  • It's unclear if smoking cannabis damages the lungs
  • Middle-aged and older people should be careful smoking weed because it could damage the heart
  • It's unclear if lung cancer risk is increased by smoking cannabis
  • Men who smoke possibly have a higher risk of testicular and prostate cancers

Some of these might sound worrying, some of them less so - but a crucial thing to point out here is that for many of these findings, the evidence is weak. A lot of studies have found correlations between smoking cannabis and the health problems listed above, but no solid causational link - Hall points out that many of these problems are also correlated with things like poverty, which tends to have a much stronger impact on (for example) how well a teenager does in school.

There's also the point to be made that a lot of the increased risks we're talking about here are less severe than the ones associated with tobacco and alcohol. A doubled or tripled chance of crashing your car if you're high sounds bad, but if you're drunk you're between six and 15 times more likely to crash. Saying that one in six teenagers will become "dependent" on the drug also sounds awful, but that's only the rate among regular users - that is, daily or near-daily smokers. That means one in six of less than five per cent of teenagers who smoke cannabis are at risk. Not great, of course, but it explains why we're not witnessing an epidemic of youth marijuana addiction, even as the strength of cannabis has increased over time. Similarly, while the risks related to mental illness get a lot of the focus, it's worth noting that the correlation between smoking tobacco and mental illness - and especially schizophrenia - is much more pronounced.

This brings us on to the second part of why the media presentation of this paper is (to put it diplomatically) unhelpful. The scientific research into the effects of drugs has rarely had anything to do with how judicial and political systems have treated those who use them, and in large part that is thanks to a systemic anti-drug culture within much of the mainstream media in the United States and Europe. (And it's ironic, considering how common recreational drug use is among journalists, as anyone who has worked in the media can attest.)

The Mail is especially bad at this - it regularly exaggerates the dangers of illegal drug use while downplaying those of legal ones, and in the process feeds into the social climate which means politicians have to take counter-productive measures to combat an invented scourge. And why not? The constituency of worried parents is always going to be larger than the constituency of drug users.

When the Mail (or any other paper with a similar stance) finds evidence that drug use can damage the human body in certain ways, it feeds into an ideology which sees the use of those drugs as a moral failing, and therefore also creates the justification for further condemnation of those people. (This is the same game that plays out whenever a single mother is pilloried for falsely claiming benefits - she becomes both a synecdoche for the failings of the entire system, and a justification for labelling everyone who legitimately claims benefits a scrounger.)

And the reverse is also true - someone criticising any aspect of the War on Drugs for its failure as a method of social control is considered to also be saying that drugs are always safe. This is in spite of the fact that nobody goes around claiming that smoking cannabis is 100 per cent safe. It's a straw man.

This is what Gallagher’s tweet is about, and it’s also why there’s a second part to the Mail’s report which isn’t about the study at all - it’s about naming the people who dared to say that maybe, just maybe, incarcerating people for smoking a plant isn't a sensible public health policy:

For years, activists and celebrities trying to decriminalise cannabis have campaigned on the claim that the real health damage to users is done by the legal ban on drugs. They have dismissed the growing evidence that smoking cannabis is a serious risk to mental health.

Prominent supporters of decriminalisation have included comedian Russell Brand, singer Sting, writer Will Self and left-wing barrister Michael Mansfield.

A key figure has been David Nutt, who was chairman of the Home Office Advisory Council on the Misuse of Drugs, until sacked for his campaigning five years ago. The professor said the risk of lung cancer from smoking was vastly greater than the risk of psychosis from cannabis.

It's interesting that papers like the Mail always target Nutt, because his career over the last decade neatly illustrates the pretence of evidence-based policy-making when it comes to illegal drugs. Nutt was fired because he pointed out that the scientific research on various drugs rarely correlated with the severity with which the legal system treated their possession and use. As chair of the Advisory Council on the Misuse of Drugs he had an obligation to point out that the government was not reflecting scientific knowledge in its policy decisions, yet he has become something of a bête noire for tabloids who relish the pun in his surname. His sacking by then-Home Secretary Alan Johnson is a neat illustration of the fallacy that there is a neat dichotomy between making policy based on evidence and making it based on moral or political principle - the science, by dint of existing within an anti-drugs political culture, became a political statement.

There's nothing wrong with scientists holding political views because of their research, and Wayne Hall, like Nutt, is no different. Hall has written a number of editorials in Australian newspapers arguing against full legalisation of drugs and treating issues like use and addiction purely as a health issue, but he's also written against the existing War on Drugs - his stance is relatively centrist. Repeatedly (like in this video) he's said that the backlash to the "exaggerations" of the dangers of cannabis over the last few decades has meant that smokers now run the risk of not believing the real risks involved when reported by scientists like him.

In this he is probably correct, though his pro-some-prohibition stance has left him unpopular with pro-legalisation reformers. (The pro-marijuana campaign group Clear has said it has submitted complaints to both Ofcom and the Independent Press Standards Organisation for claims in the press that Hall's paper said cannabis is as addictive as heroin, and it also claims Hall is a propagandist against the drug because of his links to a drug awareness body in Australia.) Regardless, it's always wise to be sceptical of reports on the dangers of recreational drugs in papers like the Mail and the Telegraph, because their ideological framework inevitably gives science the sheen of propaganda.

Ian Steadman is a staff science and technology writer at the New Statesman. He is on Twitter as @iansteadman.