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Rapid Responses: Rapid Responses published:
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What about moderation
- Sam Hilton (26 November 2002)
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Only 2 reasons for the link?
- Alison M. Curry (27 November 2002)
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old arguments
- Trevor H Turner (28 November 2002)
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Cannabis and Psychosis - data overlooked
- Alan J Gijsbers (28 November 2002)
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A Parent's perspective on the Cannabis debate
- Hugh N Roberts (1 December 2002)
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Early adolescence, cannabis initiation and psychosis
- Patrick J Keown (12 December 2002)
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Cannabis schizophrenia - does it exist?
- David H. Marjot (21 December 2002)
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Sam Hilton, Medical Student Leeds University
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It is not a surprise to hear there is evidence that cannabis usage has detrimental effects on health, especially mental health. However I think we should consider cannabis use in the same way that we consider alcohol use. Substance abuse has a negative impact on health but substance usage in moderation may not. We know that if one drinks 6 pints of lager each evening there are many negative effects. However a glass of wine each evening has been said to be good for you. It is possible that the same may be true of cannabis. Perhaps there are positive effects of consuming small amounts of cannabis on occasion and certainly it is likely there are negative effects from being under it's influence on a regular basis. It would be interesting to research other effects of cannabis usage and see if a line can be drawn between usage in moderation and abusive use. Competing interests: None declared |
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Alison M. Curry, Psychology postgrad Royal College or Surgeons in Ireland, Dublin
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Rey & Tennant propose two possible reasons for the well-established link between cannabis use and psychosis when they ask "Does cannabis cause these conditions, or do patients use cannabis to relieve their distress?" In their paper they mostly cite evidence to support the former, and to oppose the latter. This is indeed the pattern emerging from research in the area, but I would like to point out that a correlation between cannabis use and psychosis does not necessarily imply causation in either direction. I would like to see research investigating other variables, which may be responsible for the apparent link. The authors do mention studies that have controlled for use of other drugs, but a whole host of social factors including SES (socioeconomic status), and personal factors including personality, trauma, and family seem to have been entirely ignored in this review. Competing interests: None declared |
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Trevor H Turner, Clinical Director Homerton Hospital E9 6SR
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The possible association between cannabis and severe mental illness, such as schizophrenia, goes round in circles. A correspondence in the BMJ (Vol 2 1893, pp. 630, 710, 813-4, 868-9, & 969, variously entitled 'Insanity from the abuse of Indian hemp', 'Indian hemp as a cause of insanity')conducts just the same arguments as outlined by Rey and Tennant (BMJ 2002: 325, 1183-4). The robust 1893 BMJ correspondent Pyramid stated clearly that "the employment of hashish in Egypt has a beneficial effect on the almost vegetarian population". By contrast Dr Thomas Ireland, Government Medical Officer in British Guiana, considered that “the excessive use of Indian hemp […was] a very prolific cause of insanity”. The fact is that increased usage in the western world has not led to any increase in the incidence of schizophrenia (if anything it is declining), nor shown any geographically located increase. In over 20 years of inner city psychiatry I have never seen a case of ‘cannabis psychosis’, and there is no evidence of a specific or characteristic psychopathology suggesting that this is a diagnostic entity (1). By contrast, schizophrenic patients questioned about cannabis usage by our staff consistently state that they find this drug makes them feel ‘good’ or ‘calmer’, while those feeling uncomfortable, ‘bad’, or even ‘paranoid’ quickly discontinue it, for obvious reasons. Competing interests: None declared |
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Alan J Gijsbers, Specialist Physician in Addiction Studies Turning Point Drug and Alcohol Centre Fitzroy Victoria 3065 Australia
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While the BMJ editorial on the whole analyses the data well, Two most glaringly obvious observations from the original Swedish conscript study have been overlooked. That is that most of the people taking cannabis did not develop psychosis, and conversely most people who developed schizophrenia (197/41280) did not use cannabis. While the incidence in cannabis users increases, and there is a dose-response relationship (the higher the dose the greater the chance) the fact remains that out of those 2836 using 1-10 occasions only 18 developed schizophrenia (RR 1.3) 10/702 using cannabis 11-50 times developed schizophrenia (RR 3.0), and 21/752 using >50 times (RR 6.0). Clearly there is a seed-soil phenomenon and cannabis may contribute to the web of causation in some susceptible people, but cannabis by itself is not the cause of schizophrenia. Alan Gijsbers. Competing interests: None declared |
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Hugh N Roberts, Parent of a patient Not Applicable. I'm employed in the Advanced Materials Technology Industry
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This is an extract of a letter I sent to David Blunket 7th Nov 2001 (yes a year ago): Schizophrenia is the single most costly illness in the NHS budget The Cannabis of today is up to 30x more powerful than the drug used by some of our legislators during their student days 20-30 years ago. To illustrate this clearly the dosage increase is the same proportion as changing one’s alcohol consumption from a glass of wine of 1˝ bottles of Whisky. The effect and consequences of the different doses are far apart For relief to the symptoms of some medical conditions it is clear that Cannabis has benefit The issue of decriminalising Cannabis to a category C drug is the worst situation for this drug. It should either continue to be a category B drug (unworkable) or legalised with appropriate warning to users along the lines used on tobacco, for example: · ‘For people susceptible to Schizophrenia Cannabis can trigger the disease’ · The THC content of the Cannabis should also be indicated along the lines of the tar information on cigarettes today Decriminalising Cannabis may lead to increased consumption and therefore could lead to an increase in demand for treatment for schizophrenia and hence further pressure on the NHS budget Competing interests: None declared |
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Patrick J Keown, Specialist Registrar in Psychiatry Maudsley Hospital, London SE5 8AZ
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Rey and Tennant (1) discuss the strong evidence linking cannabis use (especially heavy cannabis use) with psychosis. They speculate on the importance of different developmental stages but do not elaborate on this subject. It is possible that such a process explains two recent findings: cannabis use at age 15 was more strongly associated with psychosis at age 26 than was cannabis use at age 18 (2); prisoners in England and Wales were more likely to have a functional psychosis if they had started using illicit drugs, including cannabis, before age 16 (3). This suggests that there may be a period of developmental vulnerability during which initiation of cannabis is associated with an increased rate of developing schizophrenia or a functional psychosis. However the vast majority of cannabis initiation occurs over a very short period of time. The risk of first use rapidly increases from age 11 and then rapidly decreases from age 18 until by the mid-20s the risk of initiation is minimal (4). If a period of developmental vulnerability does exist in early adolescence then it may be that later initiation of drugs (i.e. from age 18 +) is less likely to result in heavy or dependent use and may not be associated with the development of a psychosis. If this were the case it might explain the finding that Swedish conscripts with the lowest use of cannabis had the same odds of developing schizophrenia when compared with conscripts who reported no use of cannabis (5). 1. Rey JM & Tennant CC (2002) Cannabis and mental health. BMJ, 325: 1183-1184. 2. Arseneault L, Cannon M, Poulton R, Murray R, Caspi A & Moffit TE (2002) Cannabis use in adolescence and risk for adult psychosis: longitudinal perspective, BMJ, 325: 1212-1213. 3. Farrell M, Boys A, Bebbington P, Brugha T, Coid J, Jenkins R et al. (2002) Psychosis and drug dependence: results from a national survey of prisoners. Br J Psychiatry, 181: 393-398. 4. Vega WA, Aguilar-Gaxiola S, Andrade L, Bijl R, Borges G, Caraveo- Enduaga JJ et al. (2002) Prevalence and age of onset for drug use in seven international sites: results from the international consortium of psychiatric epidemiology. Drug Alcohol Depend, 68: 285-297. 5. Zammit S, Allebeck P, Andreasson S, Lundberg I & Lewis G (2002) Self reported cannabis use as a risk factor for schizophrenia in Swedish conscripts of 1969: historical cohort study. BMJ, 325: 1199-1204. Competing interests: None declared |
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David H. Marjot, Consultant Psychiatrist Retired
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My BMJ failed to arrive so I missed the contributions on cannabis until I got onto the BMJ web-site today. A disease can be fully defined by the 1. the causal agent,2 the lesion and 3. the syndrome. In the case of cannabis we are not clear about the lesion but the syndrome associated with cannabis is here called schizophrenia. Logically then we should refer to cannabis schizophrenia. The incidence and prevalence of patients showing schizophrenic syndromes are unchanged or have even fallen while the use of cannabis has increased enormously. We must conclude that either previous schizophrenic illnesses have become much less common or that cannabis schizophrenia is rare and perhaps it may not even exist. Competing interests: None declared |
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