I seem to have been reading a lot of pieces about those ‘everybody knows’ things. This hasn’t been all about one topic and it hasn’t been deliberate. It has just worked out that I’ve come across, or been directed to, a number of articles that, for their specific field of interest, demonstrate that, most of the time, what everybody knows is wrong.
This is not the first time I’ve written about this topic. Last year, I looked in detail at why people still say that coffee is a diuretic in spite of that belief coming from a poorly designed study involving just three people that, since 1928 when it was conducted, has been disproved by many other studies.
And regular readers of the blog will know that I spend a lot of time railing against the persistent myths surrounding Jacobaea vulgaris (syn. Senecio jacobaea), common ragwort. Most of those myths arise from the work of one very unreliable source but almost all efforts to present the science that demonstrates the flaws are rebuffed.
It is not just in the world of poisonous or psychoactive plants that such myths persist. Belief in homeopathy is one of the most persistent. That has been in the news in the past few days because the UK’s newly appointed health minister has been accused of being a believer. From what I’ve read, I think that attack goes a bit too far. Jeremy Hunt seems to be in the ‘where’s the harm?’ camp rather than being a true believer. There is, of course, harm in homeopathy.
For one, there have been cases where people have treated themselves, or their children, with homeopathy rather than medicine and deaths have occurred as a result. In some of those cases it has been found that the homeopathist urged the patient to turn away from effective treatments.
The other potential harm for homeopathy is financial. To work, homeopathy has to be expensive. A properly conducted trial found that people given a 20p sugar pill did not get as large a positive outcome as those told they were being given a £2 pill. (In both cases they were told there was no active ingredient in the pill but that ‘some people say it helped’.) The NHS will always be short of funds so spending money on homeopathic substances reduces the amount of money available for medicine and proper care.
What started this train of thought was a piece about something that everyone who has ever flown ‘knows’; that mobile phones and electronic devices disrupt aircraft navigation systems during take-off and landing1. The authors decided to investigate the truth of this claim after the US Federal Aviation Administration asked for public comment on its long-standing policy of demanding that devices be switched off. Interestingly, rather than look for instances where aircraft systems had been disrupted they decided to look at the number of times electronic devices have been left on and not caused any problems.
They asked 492 American adults about their last flight and found that 40% did not turn their phones off completely (presumably just switching them to silent mode), 7% left the phones fully on and 2% said they had used their equipment during take-off or landing. They then do some unexplained maths to conclude that there is only an infinitesimal chance that all the electronic equipment is switched off on any flight. I’m not sure I accept the maths but it is very clear that there are a huge number of flights where personal electronic equipment is switched on and nothing untoward happens.
That interested me because of the situation with Cannabis sativa, marijuana. Though possibly not an ‘everybody knows’, there is a claim about cannabis that gets trotted out by prohibitionists at every opportunity; 1 in 10 cannabis users becomes a problem drug user.
When I went looking for examples of that claim, I found a recently published ‘Discussion Paper’ from the United Nations Office on Drugs and Crime (UNODC) entitled ‘Cannabis: A Short Review’.2 I’ll need to read that in more detail and try and determine who UNODC expects to discuss it when it seems to have been published unannounced. But for now I just want to quote that it says ‘it is established that 1 in 10* cannabis users will become dependent’.
*Perhaps one of the things to be discussed is the internal inconsistencies. The ‘1 in 10’ figure appears on page 21 but on page 6 is says ‘It is estimated that 1 in 9 cannabis users overall will become dependent’. Clearly, there is a difference between ‘estimated’ and ‘established’ and there could be a difference between ‘cannabis users’ and ‘cannabis users overall’. Written as ‘1 in 9’ or ‘1 in 10’ the difference doesn’t seem that large but, at the top end of the UNODC annual prevalence estimate, it makes a difference of 2.5 million in the number of people said to be dependent. It is so difficult to get a clear idea of what the UNODC means that you have to wonder if they don’t want the true numbers to be easily accessed.
It is hard to know what is meant by ‘cannabis users’. The UNODC’s own World Drugs Report puts the annual prevalence of cannabis at between 119 and 224 million people. Is that saying that between 11 and 22 million people are dependent? An Australian drugs charity3 says that ‘1 in 10 people who have used cannabis are at risk of dependence’. Do they mean those who have ever used cannabis, a number far greater than those who used in the past year? And what is the difference between ‘at risk’ and ‘will become dependent’?
The easily accessible figures are for Europe and won’t apply worldwide but they show that 78 million Europeans have tried cannabis at some time, 22.5 million did so last year and 12 million did so last month. Clearly, the claim is not that monthly users are dependent since there is a 1 in 1.9 relationship between annual and monthly prevalence.
The same source, the European Monitoring Centre for Drugs and Drug Addiction (EMCDDA), says that 8.4% of the adult population (age 15-64) of the UK uses cannabis annually 3.8% monthly and 0.6% uses it more than 20 days per month. There are around 41 million adults in the UK, so 3.4 million use cannabis annually, 1.5 million use it every month and 250k use it almost daily. That’s 1 in 13 of the annual users who smoke almost daily. So, we’re already below the 1 in 10 level even if we accept the premise that everyone who smokes at least 20 days a month is a problem drug user.
You could look at the number of people who receive treatment for problem marijuana use but the trouble with that approach is that you have to use an estimate to get at the numbers of people who, allegedly, have problems with their use but don’t seek treatment. UNODC estimates that only 1 in 5 problem users seek help. I find ‘1 in 5’ to be far too neat a number to even try and see if it can be substantiated.
It looks, then, as though the ‘1 in 10’ number is not based on any reliable data but reliable data for cannabis use is pretty sparse anyway because the legal status of marijuana makes accurate data collection problematic.
But, then I remembered a recent paper about cannabis and IQ. You may have read about it because it received very wide coverage. I’m not going to go into a lot of detail about it. Except to say that it has been widely reported to be a study of 1,037 people but, in fact, results are only given for the 874 who could be followed throughout the length of the study. And, the much mentioned decline in IQ for persistent cannabis users who started in adolescence is based on 38 of those 874. So, the reported results are open to question but I’m not going to do that because I’m happy to accept the claim because it demonstrates the importance of regulating cannabis so that it is not easily available to under 18s.
To return to my point, of the 874, 242 reported that they had never used cannabis. The 38 people who were the most persistent cannabis users is therefore 1 in 16 of the 632 who had used cannabis.
But, even if you were to accept the ‘1 in 10’ claim, I think it is worth doing what the Wall Street Journal did with electronic equipment on aircraft and turning the figure upside down. If 1 in 10 people become problem users then 9 in 10 do not. And yet, the current criminal justice regime seeks to criminalise all of those people who are never going to be a problem to themselves or anyone else because of their cannabis use.
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