Royal College Of Psychiatrists “Cannabis and mental health” leaflet – a crtitique

Continuing the series of critiques of cannabis information offered by various organisations, this weeks wooden spoon award goes to The Royal College of Psychiatrists for their “Cannabis and Mental Health” leaflet.

Now lets be clear about the reason for the less than glowing critique you’re about to read. The Royal College of Psychiatrists (RC Psych as they seem to like to be called) is surely the one body above all others that would be expected to produce an informative, fact packed leaflet concerning cannabis and mental health. In all fairness, if they can’t do it then it’s hard to think of another highly respected source of information who might try.

It begins with a section headed “About this leaflet”:

Two million people in the UK smoke cannabis. Half of all 16 to 29 year olds have tried it at least once. In spite of government warnings about health risks, many people see it as a harmless substance that helps you to relax and ‘chill’ – a drug that, unlike alcohol and cigarettes, might even be good for your physical and mental health. On the other hand, recent research has suggested that it can be a major cause of psychotic illnesses in those who are genetically vulnerable.

This leaflet looks at the research on the effects of cannabis use and mental health and is for anyone who is concerned about the issue. We hope that this will help people to make informed choices about using – or not using – cannabis.

OK, fair enough although a slight alarm bell is rung by the ” genetically vulnerable” claim. There had been a theory regarding a certain manifestation combination the COMPT gene (VAL and MET types) which was a neat, simple theory that hasn’t been confirmed by recent studies. If there is a role for COMT, it’s not the simple one claimed.

Is COMT a Susceptibility Gene for Schizophrenia? Hywel J. Williams; Michael J. Owen; Michael C. O’Donovan:

In this review, we consider the evidence for and against the involvement of COMT in schizophrenia. The current data allow us to virtually exclude a simple relationship between schizophrenia and the Val/Met variant previously thought to dominate COMT function. However, recent data suggest a more complex pattern of genetic regulation of COMT function beyond that attributable to the Val/Met locus. Moreover, it is also clear that there is a complex nonlinear relationship between dopamine availability and brain function. These 2 factors, allied to phenotypic complexity within schizophrenia, make it difficult to draw strong conclusions regarding COMT in schizophrenia. Nevertheless, emerging research that takes greater account of all these levels of complexity is beginning to provide tantalizing, but far from definitive, support for the view that COMT influences susceptibility to at least some forms of psychosis.

So if there is a genetic vulnerability, it’s not obvious.

The next section is “What is Cannabis?”:

Cannabis sativa and cannabis indica are members of the nettle family that have grown wild throughout the world for centuries. Both plants have been used for a variety of purposes including hemp to make rope and textiles, as a medical herb and as the popular recreational drug.

The plant is used as:

* The resin – a brown/black lump, known as  bhang, ganja, hashish, resin etc;
* Herbal cannabis –  made up of the dried flowering tops and variable amounts of dried leaves – known as grass, marijuana, spliff, weed etc.

Skunk refers to a range of stronger types of cannabis, grown for their higher concentration of active substances. The name refers to the pungent smell they give off while growing. They can be grown either under grow-lights or in a greenhouse, often using hydroponic (growing in nutrient rich liquids rather than soil) techniques. There are hundreds of other varieties of cannabis with exotic names such as AK-47 or Destroyer.

Street cannabis can come in a wide variety of strengths, so it is often not possible to judge exactly what is being used in any one particular session.

Ganja is herbal cannabis actually, but otherwise OK and the description of skunk as just one of many varieties is fair enough. All of them if grown properly will produce a strong crop.

The last sentence is a little odd however, as the RC Psych would have been expected to give some detail about the THC/ CBD issue,  rather than to simply talk of “strength”.

Next we get a section headed “How is it used”?

Most commonly, the resin or the dried leaves are mixed with tobacco and smoked as a ‘spliff’ or ‘joint’. The smoke is inhaled strongly and held in the lungs for a number of seconds. It can also be smoked in a pipe, a water pipe, or collected in a container before inhaling it – a ‘bucket’. It can be brewed as tea or cooked in cakes.

More than half of its psychologically active chemical ingredients are absorbed into the blood when smoked. These compounds tend to build up in fatty tissues throughout the body, so it takes a long time to be excreted in the urine. This is why cannabis can be detected in urine up to 56 days after it has last been used.

It’s a pity the leaflet passes over the tobacco connection quite like this. There are many issues connected with tobacco use which one might expect the RCPsych to wish to highlight. Cannabis can’t be brewed into tea however, it needs to be dissolved into a fatty liquid first, it doesn’t dissolve in water.

A similar percentage – if not higher – of the active chemicals will be absorbed when it’s eaten, so it’s not clear what point they’re making there.

The leaflet then takes a strange turn with a large section headed “What is it’s legal status in the UK?”

Cannabis was re-classified in January 2009 and is now a Class B drug under the Misuse of Drugs Act, 1971.

The maximum penalties are:

* For possession: 5 years prison sentence or an unlimited fine, or both
* For dealing/supplying:14 year prison sentence or an unlimited fine, or both.

Young people in possession of cannabis

A young person found to be in possession of cannabis will be:

* Arrested
* Taken to a police station
* Given a reprimand, final warning or charge, depending on the offence.

After one reprimand, a further offence will lead to a final warning or charge.

After a final warning:

* The young person must be referred to a Youth Offending Team to arrange a rehabilitation programme.
* A further offence will lead to a criminal charge.

Adults in possession of cannabis

This will usually result in a warning and confiscation of the drug. Some cases may lead to arrest and either caution or prosecution, including:

* repeat offending
* smoking in a public place
* threatening public order.

Now, all that is well and good, but not at all related to the issue of cannabis and mental health. Remember we were promised that this leaflet would look “at the research on the effects of cannabis use and mental health and is for anyone who is concerned about the issue”. So far we haven’t had much of that.

The next section looks more interesting however:

How does it work and what’s the make-up of cannabis?

There are about 400 chemical compounds in an average cannabis plant. The four main compounds are called delta-9-tetrahydrocannabinol (delta-9-THC), cannabidiol, delta-8-tetrahydrocannabinol and cannabinol. Apart from cannabidiol (CBD), these compounds are psychoactive, the strongest one being delta-9-tetrahydrocannabinol. The stronger varieties of the plant contain little cannabidiol (CBD), whilst the delta-9-THC content is a lot higher.

Well, no, that is just wrong. CBD was perhaps not regarded as psychoactive at one time, but it most certainly is now. “Psychoactive is defined as

capable of affecting mental activity: a psychoactive drug

CBD has anti psychotic properties and interacts with THC to give the “Cannabis experience”. It may not produce an intoxication, but it most definitely has an effect on mental activity. For the RC Psych to make such a basic error on a leaflet like this is inexcusable.

it goes on:

When cannabis is smoked, its compounds rapidly enter the bloodstream and are transported directly to the brain and other parts of the body. The feeling of being ‘stoned’ or ‘high’ is caused mainly by the delta-9-THC binding to cannabinoid receptors in the brain. A receptor is a site on a brain cell where certain substances can stick or “bind” for a while. If this happens, it has an effect on the cell and the nerve impulses it produces. Curiously, there are also cannabis-like substances produced naturally by the brain itself – these are called endocannabinoids.

Most of these receptors are found in the parts of the brain that influence pleasure, memory, thought, concentration, sensory and time perception. Cannabis compounds can also affect the eyes, the ears, the skin and the stomach.

Now a leaflet about mental health would be expected to discuss the role of THC and CBD in some detail, in particular the moderating and anti psychotic effect of CBD on the action of THC, with perhaps some information on the role of the dopamine circuits.

The leaflet continues with What are its effects?


A ‘high’ – a sense of relaxation, happiness, sleepiness, colours appear more intense, music sounds better.


Around 1 in 10 cannabis users have unpleasant experiences, including confusion, hallucinations, anxiety and paranoia. The same person may have either pleasant or unpleasant effects depending on their mood and circumstances. These feelings are usually only temporary – although as the drug can stay in the system for some weeks, the effect can be more long-lasting than users realise. Long-term use can have a depressant effect, reducing motivation.

That was only vaguely relevant to cannabis and mental health and doesn’t even touch on the role of the THC/CBD balance, the psychedelic-like properties of cannabis, the importance of external influences on the outcome of getting stoned. It also downplays the positive effects in relation to the negative ones, which does little to explain why people use the drug. Long term use can do many things, why pick on claims of a depressive demotivation,  proof of which is thin to be polite.

All in all pretty useless really.

We then get a section on Education and learning:

There have also been suggestions that cannabis may interfere with a person’s capacity to:

* concentrate
* organise information
* use information

This effect seems to last several weeks after use, which can cause particular problems for students.

However, a large study in New Zealand followed up 1265 children for 25 years. It found that cannabis use in adolescence was linked to poor school performance, but that there was no direct connection between the two. It looked as though it was simply because cannabis use encouraged a way of life that didn’t help with schoolwork.

Perhaps slightly dodgy advice there really, and is it relevant to cannabis and mental health?

Then we get a section headed “Work”

It seems to have a similar effect on people at work. There is no evidence that cannabis causes specific health hazards. But users are more likely to leave work without permission, spend work time on personal matters or simply daydream. Cannabis users themselves report that drug use has interfered with their work and social life.

Of course, some areas of work are more demanding than others. A review of the research on the effect of cannabis on pilots revealed that those who had used cannabis made far more mistakes, both major and minor, than when they had not smoked cannabis. As you can imagine, the pilots were tested in flight simulators, not actually flying… The worst effects were in the first four hours, although they persisted for at least 24 hours, even when the pilot had no sense at all of being ‘high’. It concluded “Most of us, with this evidence, would not want to fly with a pilot who had smoked cannabis within the last day or so”.

Don’t know about you, but this almost reads like it was written by a child. Again, it has no bearing on cannabis and mental health whatsoever, what is it even doing here?

If you thought that was bad, we then go onto “what about driving?”

In New Zealand, researchers found that those who smoked regularly, and had smoked before driving, were more likely to be injured in a car crash. A recent study in France looked at over 10,000 drivers who were involved in fatal car crashes. Even when the influence of alcohol was taken into account, cannabis users were more than twice as likely to be the cause of a fatal crash than to be one of the victims. So – perhaps most of us would also not want to be driven by somebody who had smoked cannabis in the last day or so.

There is so much wrong with that section it’s hard to know where to begin. It cherry picks claims without any real context or acknowledgement of studies which produce counter results.  There are plenty of studies which show that whilst cannabis drivers are impaired they are also more careful.

That section is badly written, factually wrong and totally off subject.

Now we get back on subject with Mental health problems:

There is growing evidence that people with serious mental illness, including depression and psychosis, are more likely to use cannabis or have used it for long periods of time in the past. Regular use of the drug has appeared to double the risk of developing a psychotic episode or long-term schizophrenia. However, does cannabis cause depression and schizophrenia or do people with these disorders use it as a medication?

Interestingly they don’t look at overall rates of illness and ask “are rates of mental illness increasing in line with rates of cannabis use?” That is the sort of question this leaflet might have been expected to address and is surely the information people reading it will be looking for. Of course, there is no evidence of a rise so the point isn’t mentioned.

There is no doubt that people with serious mental illness have a less than constructive relationship with cannabis, we all know that. This information hasn’t moved the debate on at all.

Over the past few years, research has strongly suggested that there is a clear link between early cannabis use and later mental health problems in those with a genetic vulnerability – and that there is a particular issue with the use of cannabis by adolescents.

No there hasn’t. There have been theories which didn’t stand up to investigation – see above.


A study following 1600 Australian school-children, aged 14 to 15 for seven years, found that while children who use cannabis regularly have a significantly higher risk of depression, the opposite was not the case – children who already suffered from depression were not more likely than anyone else to use cannabis. However, adolescents who used cannabis daily were five times more likely to develop depression and anxiety in later life.

Again, a cherry picked bit of data and hardly representative of the knowledge base regarding cannabis and depression. For example research from Australia entitled Exploring the association between cannabis use and depression found

There was a modest association between heavy or problematic cannabis use and depression in cohort studies and well-designed cross-sectional studies in the general population. Little evidence was found for an association between depression and infrequent cannabis use.


If the relationship is causal, then on current patterns of cannabis use in the most developed societies cannabis use makes, at most, a modest contribution to the population prevalence of depression.

You pays your money, you picks your cherry.


Three major studies followed large numbers of people over several years, and showed that those people who use cannabis have a higher than average risk of developing schizophrenia. If you start smoking it before the age of 15, you are 4 times more likely to develop a psychotic disorder by the time you are 26. They found no evidence of self-medication. It seemed that, the more cannabis someone used, the more likely they were to develop symptoms.

Well, no. That is a very simplistic summary of very controversial research which claimed to show a link between cannabis use and serious mental illness but failed to show a causal connection.

Why should teenagers be particularly vulnerable to the use of cannabis? No one knows for certain, but it may be something to do with brain development. The brain is still developing in the teenage years – up to the age of around 20, in fact. A massive process of ‘neural pruning’ is going on. This is rather like streamlining a tangled jumble of circuits so they can work more effectively. Any experience, or substance, that affects this process has the potential to produce long-term psychological effects.

It should be pointed out that schizophrenia always occurs in this age group and that rates haven’t been increasing in line with cannabis use. That there is a relationship between cannabis use and schizophrenia is not in doubt, but just what that connection is remains unclear and should have been discussed on this leaflet.

Recent research in Europe, and in the UK, has suggested that people who have a family background of mental illness – and so probably have a genetic vulnerability anyway – are more likely to develop schizophrenia if they use cannabis as well.

Actually recent research in Europe – a huge study from Denmark actually entitled “Familial Predisposition for Psychiatric Disorder” – has shown there is no change at all in the profile of those people developing mental illness, whether or not cannabis is used.

There is a simple precautionary message this leaflet should be giving, which is  that children shouldn’t be using drugs at all, as they interfere with the growing brain. There’s really no need for scaremongering like this.

Physical health problems:

The main risk to physical health from cannabis is probably from the tobacco that is is often smoked with.

Well, we wouldn’t disagree with that, except of course to point out that tobacco affects the dopamine circuits of the brain and is highly physically addictive which makes cannabis use compulsive. Again, it’s off subject for the leaflet though

Is there such a thing as “Cannabis Psychosis”?

Recent research in Denmark suggests that yes, there is. It is a short-lived psychotic disorder that seems to be brought on by cannabis use but which subsides fairly quickly once the individual has stopped using it. It’s quite unusual though – in the whole of Denmark they found only around 100 new cases per year.

However, they also found that:

* Three quarters had a different psychotic disorder diagnosed within the next year.
* Nearly half still had a psychotic disorder 3 years later.

So, it also seems probable that nearly half of those diagnosed as having cannabis psychosis are actually showing the first signs of a more long-lasting psychotic disorder, such as schizophrenia. It may be this group of people who are particularly vulnerable to the effects of cannabis, and so should probably avoid it in the future.

Or alternatively that cannabis provides an early warning of the emerging illness. This is the Danish paper mentioned above – “Familial Predisposition for Psychiatric Disorder” – and makes very interesting reading. The advice offered by the researchers in their paper is somewhat different:

It is recommended that individuals with a cannabis-induced psychosis … be treated as though the condition is a first sign of schizophrenia, regardless of predisposition to a psychiatric disorder.

This leaflet seems to be advising people to simply ignore the psychotic warning and just to avoid cannabis, as if avoiding cannabis is likely to prevent a more serious condition emerging. Better, surely, to give the advice that it should be taken seriously?

Is cannabis addictive?

It has some of the features of addictive drugs such as:

* tolerance – having to take more and more to get the same effect

That is true enough

* withdrawal symptoms. These have been shown in heavy users and include:

– craving
– decreased appetite
– sleep difficulty
– weight loss
– aggression and/or anger
– irritability
– restlessness
– strange dreams.

It might have helped had they defined “Heavy user”. They are not at all usual for even long term social users.

These symptoms of withdrawal produce about the same amount of discomfort as withdrawing from tobacco.

Not for most people they don’t. That claim is hard to understand.

For regular, long-term users:

* 3 out of 4 experience cravings;
* half become irritable;
* 7 out of 10 switch to tobacco in an attempt to stay off cannabis.

The irritability, anxiety and problems with sleeping usually appear 10 hours after the last joint, and peak at around one week after the last use of the drug.

All this and yet only 1 in 10 people experience physical addiction to cannabis apparently. A large pinch of salt is required for that entire section.

We then get “Compulsive use”:

The user feels they have to have it and spends much of their life seeking, buying and using it. They cannot stop even when other important parts of their life (family, school, work) suffer.

Now this can occur with or without physical addiction. Psychological dependency is very strong with cannabis – as with many things. To be honest, this needs to be explained better.

You are most likely to become dependent on cannabis if you use it every day.

Well, maybe. It’s more a case of association between events or places and the activity of getting stoned.

But again all this seems somewhat off subject for a mental health leaflet.

What about skunk and the stronger varieties?

The amount of the main psycho-active ingredient, THC, that you get in herbal cannabis varies hugely from as low as 1% up to 15%. The newer strains, including skunk, can have up to 20%. The newer varieties are, on the whole, two or three times stronger than those that were available 30 years ago.

Oh dear, get your facts form the Daily Mail why not? Again we would have expected a discussion around the issue of CBD content, but it’s not mentioned. Does it really matter if there’s more THC in a sample if there’s a corresponding increases in CBD? It’s the low levels of CBD in at least some modern strains which is thought to cause the problems, if there are problems being caused. Why concentrate on the simplistic headline THC content?

It gets worse:

It works more quickly, and can produce hallucinations with profound relaxation and elation – along with nervousness, anxiety attacks, projectile vomiting and a strong desire to eat. They may be used by some as a substitute for Ecstasy or LSD.

Projectile vomiting? Where do they get that from? A substitute for LSD? What planet are these people on, that is just stupid.

Legally, these strains remain classified Class C drugs.

CLass B actually, thanks to Gordon.

All this rubbish and no real information about the impact on mental health, the supposed subject of the leaflet remember. We do get this however:

While there is little research so far, it is likely that these stronger strains carry a higher risk of causing mental illness. A major study currently underway, has already reported problems with concentration and short-term memory in users of stronger types of cannabis.

Clearly written before reclassification and not updated properly. The major study mentioned is probably that being undertaken by Robin Murray, which is showing the impoprtance of CBD. Again, it’s not the strength but this ratio that’s important.

Problems with cannabis use:

Many – perhaps most – people who use cannabis do enjoy it.

Oh dear, why not be honest? The vast, vast majority of users enhoy it, which is why so many people use it after all.

But it can become a problem for some people.

Yes, for a minority it can.

A US organisation, defines the problems of cannabis as follows:
“If cannabis controls our lives and our thinking, and if our desires centre around marijuana – scoring it, dealing it, and finding ways to stay high so that we lose interest in all else.”

Well, yes, that’s almost a truism.

The website carries the following questionnaire – which could equally well apply to alcohol use.

Or indeed any activity, drug or otherwise. The questionnaire asks a series of questions, answering “yes” to any one of the could mean you have a problem with cannabis apparently. “Do you find that your friends are determined by your marijuana use?” is a question nearly every stoner would answer yes to…

We seem to have moved on to something way beyond the issue of cannabis and mental health and this continues with the next section, “Reducing cannabis use”…

At this point the leaflet simply reproduces Home Office information. It’s given up any pretence here of providing an unbiased and independent examination of cannabis and mental health. Under the “Where can I get more information” it directs the reader to Talk to Frank. Is that really the best it can do?

There then follows a list of references which strangely doesn’t include the Danish Study.

The issue of cannabis and mental health is important and there’s been a lot of misinformation put about by the media and others. It was to be hoped that the RC Psych would have produced something much better than this.

8 thoughts on “Royal College Of Psychiatrists “Cannabis and mental health” leaflet – a crtitique

  1. A number of the research outcomes this quotes ,are based on studies done in NZ.
    I fear , while we might well have some top cannabis researchers who are seldom heard ,we also have some who are the best money can buy..
    Even our Govt., research ( ESR )unit has provide DUI cannabis statistics that raises the eyebrows of those more in touch with reality.

    I am afraid in NZ the need to attract research grants , usually from those with a vested interest in cannabis remaining as is may well influence outcomes.


  2. Most every eminent NZ ‘cannabis and mental health’ researcher has no truck with prohibition, a point that was loud and clear at the “Cutting Edge” conference in 2008.

    The Royal College Of Psychiatrists has been quite anal in its historical (read hysterical) “Cannabis and mental health” reporting for some time notably for failing to acknowledge ANY appreciation of or research into the settings harms, social, mental or otherwise consequent to the practice of prohibition. For that they loose my respect.

  3. It is sad to see no detail of the roles of CBD and THC, its a missed opportunity.

  4. I am also disappointed with the lack of detail regarding CBD and THC and am frequently disappointed with the multitude of misinformation produced by our government all the time on cannabis.

    I would like to suggest however regarding the possible damage that THC could cause on a developing brain that it may not matter what the THC-CBD levels are in relation to each other because although the relation probably does affect how ‘high’ you get that the possible damage being done may be only be affected by the THC level alone.

    Of course this is just a theory much like many of the statements our government produces as fact and I am not an expert on the science involved but I do think it is important that if you are on the side of legalization not to fall to the temptation of making assumptions and contextualizing evidence the way our opposers do.

  5. Hi Aaron

    Well, yes, I’m no brain care specialist, but it does seem that the ratio of THC to CBD is the important issue wrt psychosis, not simply the amount of THC alone. This comes from the two “Cannabis and mental health” conferences I attended in London in 2004 and 2007.

    Possibly of interest is the research carried out by GW Pharms for their Sativex cannabis medicine, which is a blend of cannabis types so as to give a 50-50 THC/CBD mix.

    Indeed, the concern expressed about so-called “skunk” cannabis is that it has very low levels of CBD apparently.

    Of course to an extent this is indeed theory, but it’s not “our” theory – ie cannabis law reform campaigners. It is the theory of the Psychiatrists themselves.

  6. Thanks, of course all the concern about keeping young people safe and this ‘skunk’ thing is all caused by the fact that cannabis is illegal which is so obvious but yet seems to fool so many people. When I looked at talk to frank I was shocked at how deceitful it is and the way it is worded leads me to believe a lot of time (and tax payers money) has gone into feeding us what is in many places total lies.

  7. Was someone a bit stoned and set the posting system up incorrectly so it now shows my email address even though it says (*private)

    Nice touch.

  8. I would actually agree with cannabis being linked to depression. It depresses me that I am branded either a criminal or an addict for something as safe and healthy as cannabis.

    Additionally, yes, I do make plans to get more of it which occasionally preclude doing other things. I also occasionally go down to the shop to buy things there.

    How did 1920s prohibition get broken again? I didn’t study that in history classes.

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