Select Committee on Science and Technology Minutes of Evidence


Examination of Witnesses (Questions 200-219)

PROFESSOR SIR MICHAEL RAWLINS AND PROFESSOR DAVID NUTT

1 MARCH 2006

  Q200  Adam Afriyie: You recently reviewed the link between cannabis and mental illness. How did you determine the weight of the new evidence compared to the original evidence that had informed your advice in 2002?

  Professor Sir Michael Rawlins: The evidence base had changed. Between 2002 and last year, there was a very significant change in the evidence base.

  Professor Nutt: As you may well know, a number of studies particularly from New Zealand, following groups of children who have now grown up into their 20s, and in Holland and Germany, raised more evidence that cannabis could potentially cause psychotic disorders. When you have four or five new papers suggesting that there is potentially quite a big mental health problem, a review seems reasonable—

  Q201  Adam Afriyie: Did the strength of that new evidence warrant review, in your view?

  Professor Nutt: After the 2002 report, we decided that cannabis would be a continual item on the Technical Committee's agenda. We did take evidence from one of the researchers, Stan Zanit, about a year before when he presented his new data on reassessing the Swedish conscript cohort study. We were always conscious of the ongoing research in cannabis. Then it got to the point that there were four or five papers that were pointing in the direction that there might be an increased risk.

  Q202  Adam Afriyie: Is this what prompted your review? It was not the Home Secretary?

  Professor Nutt: We have ongoing reviews but the big review that Michael chaired was prompted by the Home Secretary.

  Q203  Adam Afriyie: You first published your advice in 2002 on cannabis and mental illness. You then needed to re-evaluate that evidence base. Does that show any weaknesses in the system because you had to review it so soon afterwards?

  Professor Sir Michael Rawlins: No. It was an important area with more evidence about it. We did talk about it in 2002: could it precipitate or cause schizophrenia in vulnerable people?

  Q204  Adam Afriyie: What changed? You alluded to this in the 2002 report. Were there no experts on schizophrenia on the panel? Are you saying the evidence just was not there?

  Professor Sir Michael Rawlins: The evidence was not there. It was not a lack of experts. We had psychiatrists coming out of our ears. It was just the scientific evidence. This is a very tricky area and even now the epidemiologists that we recruited specially to advise us, on the balance of probabilities, think there is a causal link, but they are not 100% certain because there are all sorts of confounding issues that bedevil the interpretation of the evidence. One of the difficulties is, when you take the confounding issues into account, the relationship becomes smaller and smaller. Technically it is a very difficult area.

  Q205  Adam Afriyie: It seems to imply that the classification of drugs that we all read about from yourselves is dependent on the timing of when you choose to undertake a review.

  Professor Nutt: No. It is dependent on the evidence. If the evidence base changes dramatically as it did from 2002 to 2005—

  Q206  Adam Afriyie: And do you make that judgment as to whether the evidence base has changed?

  Professor Nutt: No. The evidence base did change because there were many papers published in this area. It was not a judgment call; it was a fact.

  Q207  Adam Afriyie: There was clearly a lot of media concern and confusion when cannabis was reclassified from class B to class C. Did this in any way influence your decision to leave the classification the same when you looked at it recently?

  Professor Sir Michael Rawlins: Although people say there was confusion, surveys amongst school children showed that there was not much confusion. 95 or 97% knew that it was illegal. The confusion, if anything, was in the newspapers.

  Q208  Chairman: Or in the Home Secretary's mind because he was obviously confused as well.

  Professor Sir Michael Rawlins: I could not possibly comment.

  Q209  Adam Afriyie: You are saying you do not think there was much confusion. From my understanding, looking at the papers at the time and from people I spoke to at the time, there was a great deal of confusion. Some people thought it was legal to take cannabis. Why do you think there was such confusion?

  Professor Sir Michael Rawlins: I do not know whether there really was that confusion. We have made it very clear in our second report that it is essential that people understand—particularly young people—that it is illegal. It was quite interesting, when we were having this discussion. One of our teachers on the Council said, "That in many ways is much more potent than you think. I am not sure whether I am speaking correctly or not but I say to them that if they have ever even been cautioned for possession they will not be allowed into America." She said that had much more impact than many other things that she teaches the children, the fact that they might not ever be able to visit America.

  Q210  Dr Iddon: One of the things that irritates me about the cannabis debate is that if I go into a coffee shop, as I have done but not to buy cannabis, and I have questioned the owner of the coffee shop, he will lay out all his different species of cannabis and tell you exactly what the THC content is. We talk about cannabis in this country as if it is a single substance. The fact is that the THC content of the cannabis being sold on the street has changed. Therefore, why should we keep talking about cannabis as a single substance? It is not a single substance.

  Professor Sir Michael Rawlins: No, and the strength there is 10 fold whenever it has been looked at in the material that is seized. What we do not know is what people are buying.

  Q211  Mr Flello: There are reports in the media this morning that seem to suggest that the use of cannabis in the US has plateaued or is starting to plateau but, in mainland Europe, use is still on the increase. How do you feel, if at all, the reclassification to class C has made any difference whatsoever, given that it has continued to increase since it has been changed to a C?

  Professor Sir Michael Rawlins: It has not increased. It has decreased. It has been decreasing in young people since about 1998 and it is falling at about 2% a year. That fall has continued.

  Q212  Mr Flello: That is just young people or across the board?

  Professor Sir Michael Rawlins: That is across the board, but with young people in particular it is falling at about 1% a year.

  Q213  Mr Newmark: Is there substitution in there—ie, are they taking some other drug?

  Professor Sir Michael Rawlins: Not that we are aware of. These are figures based on self-reporting behaviour, so we are reliant on that.

  Q214  Mr Flello: Do you feel that the reclassification to class C has had an influence on that?

  Professor Sir Michael Rawlins: If you look at the graph, we only have another year and the line is not a very steep curve but it is going the right way. It has not changed as a result of reclassification, but we do not know what is going to happen.

  Q215  Mr Flello: In terms of the mental illness use of cannabis, if I may widen it slightly to all drug abuse, what is your view on people who suffer from mental illnesses because of drug use or people who use drugs because they have mental illnesses?

  Professor Nutt: It is a big question. Some drugs cause mental illness. Many people with mental illness use drugs, even though it makes them worse, and we do not understand why. If we just focus for a minute on cannabis, the brain makes its own kind of cannabis. In the brain there are more cannabis receptors, targets for cannabis, than all the receptors like serotonin and adrenalin put together. There is some evidence that during the course of schizophrenia the brain's own natural cannabis substances change in relation to illness. It may be that what people are doing when they smoke cannabis is trying to restore some internal deficiency which may make some aspects of their mental state better, but in many cases it makes the psychosis worse. That is an example of the sort of complexity.

  Q216  Mr Flello: In terms of the classification of drugs and cannabis as a particular example, to what extent do you take into account the impact of people with certain types of mental health disorders using those drugs?

  Professor Nutt: It is a factor we consider when we look at all drugs because it comes into the personal life issue. Also it is a factor we look at in relation to the cost to the NHS. It is counted twice.

  Q217  Mr Devine: You said the drugs make psychosis worse. Is that evidence based?

  Professor Sir Michael Rawlins: Yes. There is very strong evidence and there is no argument amongst psychiatrists.

  Professor Nutt: That is some drugs, not all drugs.

  Professor Sir Michael Rawlins: I am talking about cannabis. In patients with schizophrenia who are in remission, cannabis will precipitate relapse. There is no doubt at all. Even I know that.

  Q218  Mr Flello: When the ACMD met to discuss the reclassification, were the same people on from the 2002 ACMD meeting present at the more recent one? Were any measures taken to exclude them?

  Professor Nutt: It was very different because we had to extend by a month the life of the previous committee to get the 2002 report fully approved. So many were coming off.

  Professor Sir Michael Rawlins: There was a big turnover after the publication in 2002. It was a rather different group. I cannot tell you how many. I can certainly let you know.

  Q219  Mr Flello: It was not ever an issue to consider about making sure there were different members on the committee?

  Professor Sir Michael Rawlins: No. A proportion will have been there previously but a significant proportion was new members who had not been involved in the 2002 decision.

  Professor Nutt: To reassure you on the ad hoc members, we brought in a number of external experts to bolster the committee. We really covered all the bases, particularly the psychiatric and the epidemiology bases.

  Professor Sir Michael Rawlins: They had not been involved in the 2002 decision.


 
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