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eLetters: Electronic letters published:
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Substance use and age at onset of schizophrenia
- Darryl Wade, Susy Harrigan (11 August 2006)
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Cannabis use and age at onset of schizophrenia
- Thomas R. E. Barnes, Hilary C. Watt, Eileen M. Joyce (9 October 2006)
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Age of onset and comorbid substance use in schizophrenia
- Rudra prosad Chakraborty, Arunima Chatterjee and C.R.J.Khess (25 October 2006)
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Darryl Wade, Clinical Psychologist ORYGEN Research Centre and University of Melbourne, Susy Harrigan
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dwade{at}unimelb.edu.au Darryl Wade, et al.
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Barnes et al (2006) examined the association between substance use and age at onset of psychosis in individuals with first-episode schizophrenia. The findings indicated that cannabis use and gender were independently associated with age at onset of psychosis after adjusting for the effects of alcohol misuse and use of other drugs. The authors concluded that the association between cannabis use and earlier onset of psychosis provides further evidence that schizophrenia may be precipitated by cannabis use and/or that the early onset of symptoms is a risk factor for cannabis use. An alternative explanation that the authors did not consider is that cannabis use has no causal influence on age at onset and that the association between cannabis use and age at onset is simply because younger patients are more likely to use cannabis. This is a plausible explanation because younger age (and male gender) is a reliable predictor of cannabis misuse in first-episode psychosis (Wade et al, 2005), and younger individuals would be expected to have an earlier age at onset of psychosis than older individuals. As a result, it should not be surprising that individuals with a comparatively younger age at onset of psychosis are at increased risk for cannabis use. Based on similar reasoning, it is possible that Barnes et al (2006) did not find a link between alcohol misuse and age at onset of psychosis because younger age is less likely to be associated with alcohol misuse compared with cannabis and other illicit substance misuse (Kavanagh et al, 2004). We would suggest that future studies need to exclude the possibility of a spurious association between cannabis use and age at onset of psychosis before concluding that the relationship may be causal in nature. Barnes, T. R. E., Mutsatsa, S. H., Hutton, S. B., et al (2006) Comorbid substance use and age at onset of schizophrenia. British Journal of Psychiatry, 188, 237-242. Kavanagh, D. J., Waghorn, G., Jenner, L., et al (2004) Demographic and clinical correlates of comorbid substance use disorders in psychosis: multivariate analyses from an epidemiological sample. Schizophrenia Research, 66, 115-124. Wade, D., Harrigan, S., Edwards, J., et al (2005) Patterns and predictors of substance use disorders and daily tobacco use in first- episode psychosis. Australian and New Zealand Journal of Psychiatry, 39, 892-898. Darryl Wade and Susy Harrigan ORYGEN Research Centre and Department of Psychiatry, University of Melbourne, Locked bag 10, Parkville 3052 Email: dwade@unimelb.edu.au |
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Thomas R. E. Barnes, Professor of Clinical Psychiatry Imperial College London, Hilary C. Watt, Eileen M. Joyce
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t.r.barnes{at}imperial.ac.uk Thomas R. E. Barnes, et al.
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Wade and Harrigan argue that the association between cannabis use and earlier age of onset of schizophrenia that we reported in our recent paper (Barnes et al 2006) may have reflected simply that younger patients are more likely to use cannabis. But the association we reported was with lifetime cannabis use at the time of presentation, a measure reflecting any previous use of cannabis, so the older onset patients might be considered to have had the same liability to take cannabis when younger as the younger onset patients. This could be assumed if the availability and social use of cannabis had remained stable, but there is a valid point to be raised about a possible ‘cohort effect’ that could have influenced the findings. For example, for older patients presenting with psychosis, cannabis use may have been less prevalent when they were in their late teens than it is now for people in that age group who might present with psychosis. However, such an effect seems unlikely to explain the size of association we found, and its impact would have been diluted by the recruitment of patients over several years. Further, there is little evidence to suggest that cannabis use in the UK by young adults has increased dramatically in recent years, and if anything there has been a gradual decrease in cannabis use in 16-24 year olds in that time (Home Office 2005, McCambridge et al 2005). Barnes TRE, Mutsatsa SH, Hutton SB, Watt HC, Joyce EM. Comorbid substance use and age of onset in schizophrenia: the west London first episode study. British Journal of Psychiatry 2006;188:237-242. Home Office. Drug Misuse Declared: Findings from the 2004/05 British Crime Survey: England and Wales, Stephen Roe, Research, Development and Statistics Directorate, 2005 McCambridge J, Hunt N, Winstock A, Mitcheson L. Has there been a decline in the prevalence of cannabis use among British nightclubbers? Five-year survey data. Drugs: Education, Prevention and Policy 2005; 12: 167–169 |
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Rudra prosad Chakraborty, Senior resident, psychaitry RINPAS, Kanke, Ranchi, India. pin: 834006; fax: 916512450813, Arunima Chatterjee and C.R.J.Khess
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rudrapc{at}yahoo.com Rudra prosad Chakraborty, et al.
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Respected Editor, We studied the article by Barnes et al. (2006) with great interest. The paper discussed a contentious issue of relation between age of onset and comorbid substance use in schizophrenia.Authors found an earlier age of onset in patients using substance, particularly cannabis. We tried to replicate the study with certain modifications. We included only drug-naïve male patients who presented to a large tertiary psychiatric facility first-time. 134 such participants of 18-60 years age were consecutively recruited after taking informed consent. Treating psychaitric units, blind to the study objectives, made the diagnoses by ICD-10 diagnostic and research criteria (WHO, 1993).Substance use history was obtained by interviewing both participants and family members. Patients with nicotine smoking were evaluated by Fagerstrom Test for Nicotine Dependence (FTND) (Heatherton et al, 1991). 86 persons (64.17%) reported using any substance. Nicotine smoking was commonest (n = 82; 61.19%), followed by cannabis (n=25; 18.65%) and alcohol (n = 16; 11.94%). 28 (20.89%) were taking multiple substances. No other substance use was reported in the study population. Participants using substance had a later age of onset of psychosis (t = 2.208; df= 132; p= .029). They were also significantly older at the time of presentation to a psychiatric facility (t = 2.948; df = 132; p = .004). Linear regression analysis revealed nicotine use (p= .023), but not cannabis (p= 0.5) or alcohol (p= 0.8) use, to be associated with a later age of onset. Linear regression analysis also revealed nicotine use, but not cannabis (p = .389) or alcohol (p = .446) use, being associated with a later age of presentation (p = .002). Further, total FTND score was significantly correlated positively with age of onset (r = .287; p= .023) and age at presentation (r= .196; p= .001) Hence, this study suggested more important role for nicotine than cannabis to predict age of onset and age at presentation of schizophrenia. Interestingly a later onset and presentation of illness in nicotine users was observed. May be the non-users were more impaired as manifested by an earlier age of onset and an earlier age of presentation. Hence they were unable to pick up the habit of nicotine smoking because of ,for example, less social interaction. Barnes, T.R.E., Mutsatsa, S.H., Hutton, S.B., et al (2006) Comorbid substance use and age at onset of schizophrenia. British Journal of Psychiatry, 188, 237 – 242. Heatherton, T.F., Kozlowski, L.T. & Freeker, R.C. (1991) The Fagerstrom Test for Nicotine Dependence: a revision of the Fagerstrom Tolerance Questionnaire. British Journal of Addiction, 86, 1119-1127. World Health Organisation (1993) The ICD-10 Classification of Mental and behavioral disorders: Diagnostic Criteria for Research. Geneva: WHO. Declaration of interest: none. |
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