Reefer Madness Dishonesty

Prof Mary Cannon

Prof Mary Cannon, arch prohibitionist

The referendum in New Zealand as to whether to re-legalise cannabis is throwing up some tired old prohibition claims. One of the latest, trumpeted by the “Say no to dope” anti law reform campaign group comes in an outrageously alarmist and virtually fact free article in the New Zealand Herald by Mary Cannon, Professor of Psychiatric Epidemiology and Youth Mental Health, with the Royal College of Surgeons in Ireland.

There is nothing worse than a scientist attempting to influence an important referendum by promoting a belief as an established fact, presenting disputed research as proof whilst ignoring the many other issues pertinent to the debate. This is the charge against Prof Mary Cannon.

The “Say no to dope” reprint is here, read it and you’ll see how utterly one sided her argument is and how she has misrepresented the current understanding of cannabis and mental illness to feed the reefer madness hype. “Say no to dope” were only too happy to make use of all this.

Don’t get me wrong, I’m not dismissing valid concerns about the effect of cannabis on a small number of people, but to imply as she does that cannabis use is the major and growing cause of psychosis is patently untrue.

Having partially acknowledge the harm alcohol can do she writes

In fact, cannabis use is now the most powerful single environmental risk factor for psychotic disorder.

Prof Mary Cannon, NZ Herald

She really is claiming that cannabis is a greater environmental risk factor than child-rearing experiences, head injury and possibly child abuse for example? That’s some claim and of course it’s nonsense. To justify this she refers to several studies including the Dunedin study where she claims

The Dunedin study showed that young cannabis users had lower incomes later in adulthood than their alcohol using peers. Heavy, early onset cannabis use has been associated with up to 8-point drop in IQ that appears to be irreversible.

Prof Mary Cannon, NZ Herald

Although not entirely discredited, the Dunedin study has been highly criticised flawed methodology and for drawing a causal inference from the results (Correlations between cannabis use and IQ change in the Dunedin cohort are consistent with confounding from socioeconomic status)

A simulation of the confounding model reproduces the reported associations from the Dunedin cohort, suggesting that the causal effects estimated in Meier et al. are likely to be overestimates, and that the true effect could be zero

Ole Rogeberg

She makes several misleading claims, in short, she presents an open and shut case about an issue which is still highly debated and far from proven and uses it to oppose cannabis law reform. For an academic to do that is simply unacceptable, nothing short of a disgusting deception.

That would be bad enough. But she leaves the most dishonest claim till last

No one would deny that alcohol is associated with a host of social problems and serious physical health problems.

However, I would argue that cannabis use is actually more damaging to the brain – especially the brains of young adults and teenagers, and their life prospects.

Prof Mary Cannon, NZ Herald

And from this unbelievable conclusion she states

Once society normalises the widespread use of a drug it is almost impossible to undo that and put the genie back in the bottle.

Prof Mary Cannon, NZ Herald

That is a the big prohibition lie and it is built on two false assumptions:

1: Prohibition actually works and prevents widespread use of a substance, bringing about the lowest level of use.
2: That the lowest level of use automatically represents the least possible harm

Neither assertion is necessarily true.

Prohibition makes studying the illegal drug culture difficult if not impossible. In particular it is not possible to know with a high degree of certainty just what the level of use of a drug is in society. It can be inferred, but it can’t be measured. As any respectable scientist will tell you, a study based on unreliable data us little more than cod science: The rule is garbage in = garbage out.

But what we do know is that prohibited cannabis use is widespread, indeed in some parts of society it is totally normalised and has been for decades, the smell of cannabis drifting across parks is familiar enough. Prohibition, quite simply, does not deter people who want to use it from doing so. The point being that prohibitionists cannot demonstrate that prohibition produces the lowest level of use and their belief that it does is just that, a faith based belief, nothing more.

The second point is perhaps more damning: The lowest level of use does not equate to the lowest level of harm necessarily. To explain that we only have to look to prohibition era America and what happened with alcohol. Prohibition was quite good at reducing the overall use of alcohol, but the harm from consuming moonshine was far worse than allowing legal booze. Not only was the physical and mental harm from consuming that drug worse, but so was the harm to society as the policy fuelled the organised crime gangs who supplied it.

We know from the experience of 1920’s America with alcohol and we know it from modern day experience with the failed war on drugs. Prohibition itself creates huge levels of harm, not just for the consumers but for the whole of society. Prof Cannon ignores all that as she presents her one sided skewed support for prohibition.

A legal regime would create the opportunity to protect the vulnerable whereas prohibition can provide no such protection, arguably putting the vulnerable at the greatest risk. It may be called “drug control” but there is no control over the illegal supply of cannabis, no control over strength, purity, THC/CBD content, who sells it, where from and no age restriction. Under prohibition cannabis is not a controlled drug in any sense of the word and prohibition is demonstrably harm maximisation. All the research done under prohibition is of course research looking at illicit use of an illicit product, of course you will see elevated levels of harm. Any study that looked at alcohol during prohibition would have concluded it was an even more damaging drug than it is under a legal regime. The same logically applies to cannabis.

The claims of mental illness derived from cannabis use are actually a strong argument against the unregulated regime of prohibition. If they are true then the commercial trade should be properly controlled and regulated, if the claims are true then the proportion of THC to CBD should be at least known if not limited and there should be an age limit for sales. This is easy to do under a legal regime, impossible under prohibition.

All that said there is a good argument for being opposed to commercial exploitation of the trade – advertising, branding etc. UKCIA has long opposed the free market exploitation of cannabis (and other drugs including alcohol). Cannabis has a natural demand in society, there is absolutely no need to advertise and promote the product. If Prof Cannon were to engage with that argument, she might be worthy of some respect but ensuring it is only available with zero quality control and supplied by organised crime is illogical at best, dishonest at worst.

It can not only be argued that the lowest level of harm would occur with a properly regulated supply side, but there is a strong argument to suggest that the lowest level of use would occur when the natural demand in society is supplied with no promotion or commercial encouragement to recruit new users. The thing is, we would know the level of use and the nature of any harms, exactly.

This argument can be summarised from this graphic taken from “The paradox of prohibition” by John Marks

Making drugs available to those who will use regardless, reduces the need to trade to finance their use of drugs. The prolific epidemic quality of prohibition is thus undermined. If drugs are made too readily available, the minimum is passed and use starts rising again, as may be seen today with alcohol.

John Marks


UKCIA is a cannabis law reform site dedicated to ending the prohibition of cannabis. As an illegal drug, cannabis is not a controlled substance - it varies greatly in strength and purity, it's sold by unaccountable people from unknown venues with no over sight by the authorities. There is no recourse to the law for users and the most vulnerable are therefore placed at the greatest risk. There can be no measures such as age limits on sales and no way to properly monitor or study the trade, let alone introduce proper regulation. Cannabis must be legalised, as an illegal substance it is very dangerous to the users and society at large.

2 thoughts on “Reefer Madness Dishonesty

  1. This article makes the case for legalisation perfectly. I can’t fault your reasoning in any way and agree wholeheartedly.

  2. Erudite as ever Derek but I feel sorry for those poor Kiwi prohibitionists who went to great lengths to devise a rhyming name for their campaign ‘Say Nope To Dope’ and you took it away from them by truncating ‘Nope’ to a boring old ‘No’.

    Not content with utterly demolishing the delightful Mary’s argument, you had to stick the knife in as well. You brute, you! 😉

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