Tuesday 3rd February saw a programme in the BBC’s “Horizon” series entitled “Cannabis: The Evil Weed?”. The BBC website offered the following summary:

Cannabis is the world’s favourite drug, but also one of the least understood. Can cannabis cause schizophrenia? Is it addictive? Can it lead you on to harder drugs? Or is it simply a herb, an undervalued medicine?

Addiction specialist Dr John Marsden discovers that modern science is finally beginning to find answers to these questions. John traces the cannabis plants’ birthplace in Kazakhstan; finds the origins of our sensitivity to cannabis in the simple sea squirt; and finds out just what it does to our brains.

He meets people who have been changed by this drug in drastically different ways – from those whose lives have been shattered to those who lives have been revived.

The programme started, as they so often do, with a taster of what was to follow. We were told that cannabis “produces a range of effects that is unmatched” which is probably fair enough. We then met three people – a cannabis user who loved the drug as “being better than sex”, an addict who was “ruled” by cannabis and someone who used it at a young age and went on to develop schizophrenia. Then we heard sound bites from three scientists and a piece to camera from  Dr John Marsden who poses the question “what does science reveal about the world’s favourite drug?”

So as usual, cannabis was regarded in a way alcohol and tobacco aren’t – as a “drug”. Hence the claim that cannabis is the  “world’s favourite drug”, which if course is simply not true, cannabis comes in at number 4, behind alcohol, nicotine and caffeine. This blindness to the real nature of the legal drugs was to produce a major failing in the programme, which we will come to later.

A second major failing was that no comment was made about the effect of the law on the gathering of scientific data regarding cannabis. Of course, had this been a programme about alcohol, we would have seen population studies and so forth. There could of course be non for cannabis, the reason being due to its legal status which makes such studies impossible. Of course the prohibition law has been responsible for many aspects of the cannabis trade and culture and has created many aspects which simply would not have otherwise existed, yet it was never mentioned.

In addition, although the fact that cannabis varies in its composition and contains more than one important ingredient was mentioned in the introduction, this important variable was not mentioned again until near the end and all the studies which claimed to show what cannabis actually does were in fact carried out only with THC. Now the real cannabis experience is not simply THC and so how far these results can be applied to the real world is very much open to debate, but the programme did not acknowledge this. As a factual scientific programme this sort of omission is a serious criticism.

The first section was pretty interesting, Dr John Marsden explained that he was an addiction specialist who worked with heroin and cocaine addicts and that compared with these drugs, the effects of cannabis were “a walk in the park” and that the number of its users eclipsed the users of all the other drugs put together. He told us that he had used cannabis himself but guess what – like many a politician he didn’t enjoy the experience! At least he accepted that he could see the attraction, but had decided “cannabis was not for him”, so fair enough.

We were introduced to the fact that cannabis has been around for thousands of years, we were told how THC works in the brain and why we have come to have the receptors in our brains which THC binds to along with what they are there to do. We also had some interesting information about how we evolved from the sea squirt. Again, all good stuff.

Then we start to look at how modern science is investigating the way cannabis actually works and from here on, “cannabis” becomes simply “THC”. We were told how the brains cannabinoid chemicals “dim” the flow of other messenger chemicals, which is how the brain regulates its behaviour. We were shown research in the USA which identified where the THC receptors were and how widespread they are throughout the brain – hence the wide range of effects of cannabis.

A couple of cannabis users explained the sensation they enjoyed by way of illustration. Dr John Marsden explained there was nothing very unusual about cannabis containing chemicals that do this and cited the opium poppy and tobacco amongst others as having chemicals which “act on the brain”. It was now the question “how real is the dark side of cannabis” was posed.

Is cannabis addictive?

We were introduced to another “John” – someone who didn’t want to use their real name, but was happy to appear on TV, which seemed more than a little illogical. “John” considered himself a cannabis addict, someone who had given up his life to cannabis. We were given a quite depressing account of how this guy’s life had become dominated by  the need to roll a spliff, morning noon and night. “John” also seemed amazingly bad at rolling a joint, something most heavy cannabis users can do blind folded.

This is where the programme fell down badly, and for an addiction specialist it was very strange  the Dr John Marsden – who had already mentioned the fact that tobacco contains a mind altering drug did not pick up on this. “John” the addict was smoking cannabis mixed with tobacco and described a typical tobacco habit. Could it be that his addiction was actually fueled by the tobacco addiction, with him not realising – or wanting to admit to himself – that he was in fact a heavy tobacco addict? We were given the impression that he only smoked joints, never cigarettes, is this the case? For any scientist to present an case example like this without pointing out blindingly obvious confounding factors is really quite inexcusable.

However, the programme went on to explain that cannabis is not physically addictive and that “John’s” apparent addiction was probably psychological. It was pointed out that psychological addiction can be difficult to beat which is true, but why didn’t they also mention the complicating factor of the tobacco and it’s very definite physical addiction properties which include strong cravings? Dr John Marsden used the word “craving” to describe the psychological urge to use cannabis, it’s highly questionable if any such cannabis craving even remotely compares the that of tobacco.

The programme entirely avoided any consideration of the tobacco issue, which is important not just for the addiction potential but also for a range of other health issues. Why did it do this?

We then moved on to the accusation often leveled at cannabis that it’s a “gateway” drug to hard drug addiction:

Does cannabis “lead on” to other drugs?

Here would have been a useful time to have referred to  proper population studies. Of the millions of cannabis users world wide, how many do actually go on to become heroin or cocaine addicts? Of course, because of prohibition we simply don’t have those population studies and we can’t get them. Although this problem created by prohibition wasn’t referred to directly, he explained the use of lab rats because “unlike humans we can give them cannabis in controlled amounts” to see what happens. It’s assumed that the rat’s brain structure is similar enough to ours to be able to extrapolate from.

Whatever the merits of doing unnecessary experiments on animals like this (there are, remember millions of willing human volunteers who take cannabis whether they’re studied or not)  the conclusion was that cannabis users are no more likely to become heroin addicts than non-users, cannabis is not a gateway drug.

The conclusion made by the programme was that it’s more “likely to be peer pressure or life stresses that lead people onto harder drugs”. The fact that cannabis users are much more likely to be offered other drugs by their unregulated prohibition created dealer than non-users wasn’t considered.

Does cannabis trigger permanent psychosis or schizophrenia?

We were introduced to  Paul and his family. Paul has schizophrenia and was a cannabis user at a young age and his parents put the condition down to his early cannabis use. We were given a fair description of what severe mental illness is and we were told that Paul is now on the road to recovery and has stopped his cannabis use.

The fact that his cannabis use was unknown to his parents – a very common  thing given the “underground” nature of its illegal use – was mentioned but not followed up with any difficult questions which might have raised the issue of the law’s role.

However, Dr John Marsden went on to explain that although it might seem an obvious link exists, in fact it’s much harder to demonstrate as it’s a “chicken and egg” situation. Does cannabis cause mental illness, or do ill people seek it out (ie find it in some way especially appealing). Again, some real life population studies would help us to understand what’s going on, but again  because of the law they don’t exist.

So were shown some experiments with mice using the Maurice water maze , some of which were given cannabis at an early age, some later. The mice were put in a bowl of water and had to swim to a tower, the surface of which was just below the water level – the water being cloudy to prevent the mice seeing the tower. The mice had been shown the tower before and should know where it is by reference to objects outside of the tank. The experiments showed that mice given cannabis at an early age (<15 in human terms) showed learning impairment and couldn’t find the tower, whereas those given cannabis at a later age found it quickly, showing no impairment with a control group. The conclusion from this is that it’s probably not a good idea for people under 15 or so to consume high levels of THC, but for those above that age there’s no impairment. The researcher made the point that the number of children using cannabis is increasing, yet no explanation as to why this is happening was considered nor why there can be no protection for children under the present regime – again, no consideration of the impact of prohibition.

Dr John Marsden made the point that the risk of schizophrenia is low at around 1%, but then made the claim that occasional use of cannabis can raise this to 2% and heavy use might raise it to 6%. No source for those figures was given and no population data is available to support them, but it was stated as fact.

We then moved on to  the research by DR Zerrin Atakan which is looking at the role of THC in the brain which has been mentioned before on this blog.  The conclusions are that the effects of THC are similar to the effects of schizophrenia which re-enforces the idea that smoking cannabis can, in a small number of cases, trigger the condition.

Now this is the point where we really need proper population studies. Over the past 40-odd years cannabis use has increased massively. Not mentioned in the programme was the research carried out by the ACMD as a part of its review of cannabis classification for the Home Office (and still not published) which seems to show a decrease in  rates of schizophrenia in this time. The lack of real hard data is a serious impediment to understanding what’s really going on, but this wasn’t referred to yet again.

Is cannabis a medicine?

The programme then looked at the medical dispensary system in California, which to be frank looks very much like legalised cannabis. The range of conditions a doctor can prescribe cannabis for is wide to put it mildly and probably anyone who wants it can get it. Dr John Marsden did question whether this is real medical use, but didn’t produce any evidence of it’s ill effects – other than being in conflict with state law.

We then  looked at the development of SATIVEX, the cannabis derived medicine being grown at the secret location known as Porton Down. Only now was the existence of CBD and its anti psychotic properties mentioned, and the claim made that someof the newer recreational strains contain no CBD at all (which isn’t actually correct, although CBD levels are low in some strains). A good case for the proper regulation of the commercial trade was almost made, but avoided.

So the end of the programme and anyone who expected an answer to the question it posed: Is cannabis the evil weed? was in for a bit of a shock. Dr John Marsden’s opinion was this:

Cannabis isn’t in the same league as heroin and cocaine. It can’t kill you and is very unlikely to ruin your life”. He went on to say that “cannabis use has no place in the developing brain and although the numbers of people affected is tiny, there does appear to be a link between the early use of cannabis and mental health problems”. Now, it would have been expected that Dr John Marsden would have concluded his presentation with the advice that cannabis should be restricted to adults, much as we do with alcohol, but no. He concluded with a quite shocking and un scientific opinion:

“… in the end it’s my impression that the most significant damage caused by cannabis is subtle. It’s not at the extremes, it’s the thousands of regular smokers who’s lives are held back, it’s the apathy, it’s the sitting around smoking, not getting things done, the valuable, precious opportunities of life are lost”. Cue emotive music, programme ends.

So much for the promised objectivity.

It was as if the BBC had instructed Dr John Marsden to end on a downbeat note of doom about cannabis use and that was the best he could come up with. In all honestly , this conclusion debased what had been quite a good programme, albeit compromised in places.

Is cannabis the evil wed? From the evidence in the programme, no it’s not in all honestly, although as with many things in life it does need a proper regulated framework to minimise harm to vulnerable groups like children. One programme like this can’t be expected to cover every aspect of an issue as complex as cannabis, but it did miss out several vitally important issues that really should have been at the very least considered. In it’s favour though it didn’t feature the “usual suspects” making their usual claims.

It would be interesting to see a similar programme made about alcohol  and it’s effects – not as the controlled and regulated drug as we have now, but under a regime of prohibition similar to that which cannabis exists under. I wonder how the two would compare?


Horizon: Cannabis – the evil weed? can be seen (in the UK) on the BBC i-player for the next 70 days or so here and will be repeated on 14th February at 01:15 on BBC One (except Wales).