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Last Updated: Sunday, 19 June, 2005, 21:23 GMT 22:23 UK
Cannabis and psychosis
Dr Philllip Robson
Dr Philip Robson, Director of the Cannabinoid Research Institute, is an expert on the therapeutic potential of the components of cannabis. In 1996 he was commissioned by the Department of Health to carry out a critical review of the relevant scientific literature and in 1998 was called on to submit both written and verbal evidence to the House of Lords Science and Technology Committee investigation into cannabis.

Dr Robson says that although cannabis is a drug that has a 5,000 year history of use by humans, the amount of really carefully gathered scientific information about it is relatively limited in humans. He is interested in the potential of cannabis as a medicine for a wide range of medical conditions. He doesn't say that it is a wonder drug but simply that it probably has a place in modern therapeutics, alongside existing standard medicine. He is convinced that "in the future there will be a role for cannabis-based medicines in areas of medicine alongside the standard medicines which are not performing as the patient deserves at the moment."

The following is an edited transcript of Panorama's interview with Dr Robson in which he answers questions about cannabis and mental illness.

What is cannabis, what are the active ingredients?

I think it's a fascinating plant and it's one that historically has been very useful to humans. I think it's very important that we don't throw it away just because it's now a pariah drug as a result of its recreational use... It's a wonderfully interesting hotchpotch of hundreds of different chemicals, more than 60 of which in fact, are unique to the plant, they're called cannabinoids. THC is the best known of all, that's the psychoactive one that recreational smokers treasure.

Then there's CBD which has all sorts of interesting interactions with THC but many interesting properties in its own right, medicinal properties that is, such as anti-inflammatory, pain relieving, antispasticity, you know.. antipsychotic potentially, even neuroprotective And then all these other cannabinoids have hardly really been examined yet. And then there are lots of other plant components like turpenoids and phenols which when you look at them as individuals also have some intriguing potentially therapeutic activities like anti-inflammatory, anti-bacterial, all sorts of things that they are capable of doing independently.

It's a wonderfully interesting hotchpotch of hundreds of different chemicals, more than 60 of which in fact, are unique to the plant, they're called cannabinoids
And then of course there's the combined effects of all these things what you might call the synergistic effects that people are only really now just beginning to explore. I think some researchers have referred to them as an entourage effect, that some vital chemical within the plant can't do its full job unless it's surrounded and supported by a whole lot of support acts, a whole lot of... the orchestra if you like, the supporting instruments. I don't know whether that will be provable in time and in science but it's certainly an intriguing theory, and of course there are... there's good evidence about the interaction between CBD and THC but these other interactions are very much in their infancy.

So how much is known about cannabis, I mean how much has been known over the years about cannabis and its effects?

The medicinal use certainly goes back several thousand years and has found a place in virtually every pharmacopoeia throughout the world actually at some time. It came of course to Europe relatively late, mainly in the 19th century, sprang into prominence, and by the middle of the 19th century actually it became one of the most fashionable drugs to use, and then gradually went into decline for various reasons, I mean cannabis could be purchased from the grocer, and that really was very unpopular with doctors and pharmacists. So as synthetic medicines became more available, as other means of giving medicines became more available, like the hypodermic syringe, so there would be a move towards that area and a move away from plant medicines.

The medicinal use certainly goes back several thousand years and has found a place in virtually every pharmacopoeia throughout the world actually at some time
But then the huge breakthrough comes in the 1980s of the discovery of the endocannabinoid system with its receptors, its endogenous ligands, it's the bodies own cannabinoids and how they influence normal physiology and may impact on a whole range of diseases.

I think it's full role is only now being uncovered frankly, but it clearly has a role in cognition, in sort of interpreting the world in movement, in the appreciation of pain, in the control of a whole host of different organ systems to be honest, in a very subtle way...

Some people will be surprised that we have a system that is designed to be responsive to the active ingredients of cannabis. Have we somehow evolved with cannabis?

That's a very interesting one. I mean people have looked into this and there is some fascinating work being done. I think it's probably the case that the receptor system predates the plant in the world but we're talking millions of years back in both areas. It seems to be just a serendipitous interaction.

But no, the cannabinoid receptor was there long before the plant was available, but we have tapped into it, much as we've tapped into the opium poppy to take benefit of the opiates.

How much is known about the medicinal properties of cannabis?

It's very much an emerging science clinically. A very large number of what you might call "pioneer studies" were done in the 20th century, but it's only recently that proper randomised control trials have been undertaken.

If you've got a range of symptoms, not just pain but perhaps nausea, loss of appetite, weight loss, feeling pretty bad about life and the future, a drug which can actually impact several of those symptoms at the same time is potentially particularly useful, and it's also notable that the standard treatments for many of these diseases is very unsatisfactory, either because it only provides partial relief of symptoms like spasticity or because it's potentially very toxic, and that's the position that a lot of people with multiple sclerosis find themselves in actually: that they're taking all the available treatments that are around, but still they have unacceptable levels of spasticity, pain and other symptoms.

If you've got a range of symptoms, not just pain... a drug which can actually impact several of those symptoms at the same time is potentially particularly useful
Patients have been telling us frankly for decades, which is that there are a number of conditions which standard treatments do not deliver the answer at the moment which cannabis seems to be able to help to a certain extent.

I'm not saying it's a wonder drug, I'm simply saying that it probably has a place in modern therapeutics, alongside existing standard medicine. I'm convinced that in the future there will be a role for cannabis-based medicines in areas of medicine alongside the standard medicines which are not performing as the patient deserves at the moment.

There appears to be growing evidence of a close link between the use of cannabis particularly by adolescents and the development of psychotic illness. What role do you think cannabis is playing in the development of psychotic illness?

Well can I say first of all I think that there's a clear consensus that smoking cannabis if you already have a mental illness is likely to make that worse. So let's take that as read because going on from that, there's an emerging literature which seems to suggest that it may actually be an independent risk factor to schizophrenia.

Terms like psychotic symptom, psychosis, schizophrenia, represent very different things but they seem sometimes to be used interchangeably
One has to take this research very seriously, but I think we do need to be cautious in interpreting it because it has a number of difficulties - there are a small number of studies that can be used to, as it were, base this association, less than ten, certainly, and one of the things I think which we have to start off by concerning ourselves about is a problem of definition. Terms like psychotic symptom, psychosis, schizophrenia, represent very different things but they seem sometimes to be used interchangeably.

A psychotic symptom is really a misinterpretation of reality. So for example, if I think someone is looking at me strangely, but there's no evidence for that, that could be psychotic symptom. A psychosis is a bunch of those symptoms which causes me to lose touch with reality.

And then schizophrenia is at the other end of the scale as the most devastating psychosis, one which is involved in with abnormalities of perception, emotion, thought, motivation, motor function, which devastates people's lives and has a terrible prognosis.

But they're not all the same thing at all and I think one thing that concerns me in the research which usually focuses on psychotic symptoms is the assumption that that equals a risk of schizophrenia. The next point is that it's been established for millennia that cannabis can produce as part of intoxication psychotic symptoms. These are generally transient and pass away as the drug is metabolised from the body.

Do you think there's any link between the possible antipsychotic properties of cannabis and the fact that many patients with mental illnesses do like to use cannabis?

I think the answer is that no one really can explain the observation that many more people with psychosis do seem to smoke cannabis than the general population. CBD maybe have an impact, it may be that somehow they just feel better in the conditions that they found themselves in which often, after all, are pretty unpleasant being in a mental institution or being very scared by the experiences that you're having. Perhaps the drug makes them feel more relaxed.

no one really can explain the observation that many more people with psychosis do seem to smoke cannabis than the general population
There is an intriguing observation made by a psychiatrist in Africa that where the black market cannabis contains more CBD, it seems that cannabis-related psychotic episodes seem to be less marked than in areas where the street cannabis contains very little. Just an anecdotal observation but it all adds to this intriguing possibility that CBD may have, in the end, a role in the treatment of psychosis.

So what is it about cannabis do you think that links it with psychotic symptoms because you say there is a strong link between cannabis and the development of temporary psychotic symptoms associated with it?

I think that one of the very important things to consider is the context in which the drug is taken. If people are feeling relaxed, unthreatened, congenial company, know what to expect, they will interpret a particular symptom in a very different way to someone who is feeling depressed, fearful, in a dreadful... um... dreadful surroundings, and the same symptom could have very different meaning for those two different people.

I think that one of the very important things to consider is the context in which the drug is taken... the same symptom could have very different meaning for those two different people
It's very context related. If I'm a 14 year old smoking lots of cannabis, I'm basically participating in an illegal activity which is going to have many other effects potentially in my life, my family are not going to be very pleased with this problem. I may even fall out with my family completely. I may drop out of schooling or do very badly at school. I may be involved with a bunch of friends who are much less constructive than would otherwise be the case. I might be involved in other delinquent activities.

All of those things that I've mentioned have a proven association with future mental illness and may not register in the research which is being done looking at the cannabis. So whilst I'm not saying that there isn't an association between cannabis smoking and the risk of later psychotic symptoms, I'm saying that there are a number of issues that perhaps lessen the power of that association in the existing research.

Whilst I'm not saying that there isn't an association between cannabis smoking and the risk of later psychotic symptoms, I'm saying that there are a number of issues that perhaps lessen the power of that association in the existing research.
I mean, I would like to say though, that all my instincts are that smoking cannabis or in fact using any psychoactive drug when your brain is still developing is terribly undesirable, and very much to be argued against.

Does Cannabis lead to the development of schizophrenia?

Having accepted that cannabis can actually cause acute psychotic symptoms in the context of intoxication it's very important in the research that's done to discriminate that from the longer term insidious functional psychotic symptoms that occur typically in schizophrenia.

Some of the studies have tried to do this, not all, some of them have tried to do it but of course in order to do that you can only ask the person have you been smoking cannabis recently. There are no objective tests to rule that out. So if for example at the end of the study I'm a 25 year old and I'm being given a questionnaire of psychotic symptoms and I tick one of them and then find I'm labelled as psychotic, if I don't choose to tell the investigator that actually I did smoke a spliff last night, that effect could entirely be a transient toxic effect and not related to the much more sinister chronic psychosis that the investigators are interested in.

At the moment a causal link between cannabis smoking and schizophrenia has not been established
And just finally I would say that if there was a very strong association between smoking cannabis as a youngster and developing schizophrenia in later life, and I mean schizophrenia rather than psychotic symptoms or psychosis, then you would expect that if you were to monitor very carefully the rate of cannabis smoking in a particular country where you could show that it was going up very markedly, then you would expect to see the prevalence of schizophrenia going up markedly too.

That hasn't been seen where it's been carefully looked for, for example, in Australia. So I think one has to say that this is an association which requires very careful future examination. But at the moment a causal link between cannabis smoking and schizophrenia has not been established.



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